U.S. patent application number 15/920616 was filed with the patent office on 2018-10-04 for magnetic tape.
This patent application is currently assigned to FUJIFILM Corporation. The applicant listed for this patent is FUJIFILM Corporation. Invention is credited to Norihito KASADA, Eiki OZAWA.
Application Number | 20180286443 15/920616 |
Document ID | / |
Family ID | 63671821 |
Filed Date | 2018-10-04 |
United States Patent
Application |
20180286443 |
Kind Code |
A1 |
OZAWA; Eiki ; et
al. |
October 4, 2018 |
MAGNETIC TAPE
Abstract
The magnetic tape has the total thickness of a non-magnetic
layer and a magnetic layer of 0.60 .mu.m or smaller, the magnetic
layer including an abrasive and fatty acid ester, a percentage of a
plan view maximum area of the abrasive confirmed in a region having
a size of 4.3 .mu.m.times.6.3 .mu.m of the surface of the magnetic
layer with respect to the total area of the region, obtained by
plane observation performed by using an SEM of 0.02% or greater and
less than 0.06%, full widths at half maximum of spacing
distribution measured by optical interferometry regarding a surface
of the magnetic layer before and after performing a vacuum heating
with respect to the magnetic tape of greater than 0 nm and 7.0 nm
or smaller, and a difference between spacings before and after the
vacuum heating of greater than 0 nm and 8.0 nm or smaller.
Inventors: |
OZAWA; Eiki;
(Minami-ashigara-shi, JP) ; KASADA; Norihito;
(Minami-ashigara-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
FUJIFILM Corporation |
Tokyo |
|
JP |
|
|
Assignee: |
FUJIFILM Corporation
Tokyo
JP
|
Family ID: |
63671821 |
Appl. No.: |
15/920616 |
Filed: |
March 14, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G11B 5/70 20130101; G11B
5/78 20130101; G11B 5/70615 20130101; G11B 5/71 20130101; G11B
5/70626 20130101; G11B 5/00813 20130101 |
International
Class: |
G11B 5/706 20060101
G11B005/706; G11B 5/008 20060101 G11B005/008 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 29, 2017 |
JP |
2017-065751 |
Claims
1. A magnetic tape comprising: a non-magnetic support; a
non-magnetic layer including non-magnetic powder and a binding
agent on the non-magnetic support; and a magnetic layer including
ferromagnetic powder and a binding agent on the non-magnetic layer,
wherein a total thickness of the non-magnetic layer and the
magnetic layer is equal to or smaller than 0.60 .mu.m, the magnetic
layer includes an abrasive and fatty acid ester, a percentage of a
plan view maximum area of the abrasive confirmed in a region having
a size of 4.3 .mu.m.times.6.3 .mu.m of a surface of the magnetic
layer with respect to the total area of the region, obtained by
plane observation performed by using a scanning electron microscope
is equal to or greater than 0.02% and less than 0.06%, a full width
at half maximum of spacing distribution measured by optical
interferometry regarding the surface of the magnetic layer before
performing a vacuum heating with respect to the magnetic tape is
greater than 0 nm and equal to or smaller than 7.0 nm, a full width
at half maximum of spacing distribution measured by optical
interferometry regarding the surface of the magnetic layer after
performing the vacuum heating with respect to the magnetic tape is
greater than 0 nm and equal to or smaller than 7.0 nm, and a
difference S.sub.after-S.sub.before between a spacing S.sub.after
measured by optical interferometry regarding the surface of the
magnetic layer after performing the vacuum heating with respect to
the magnetic tape and a spacing S.sub.before measured by optical
interferometry regarding the surface of the magnetic layer before
performing the vacuum heating with respect to the magnetic tape is
greater than 0 nm and equal to or smaller than 8.0 nm.
2. The magnetic tape according to claim 1, wherein the percentage
of a plan view maximum area of the abrasive confirmed in a region
having a size of 4.3 .mu.m.times.6.3 .mu.m of the surface of the
magnetic layer with respect to the total area of the region,
obtained by plane observation performed by using a scanning
electron microscope is 0.02% to 0.05%.
3. The magnetic tape according to claim 1, wherein the total
thickness of the non-magnetic layer and the magnetic layer is 0.20
.mu.m to 0.60 .mu.m.
4. The magnetic tape according to claim 1, wherein the full width
at half maximum of spacing distribution measured by optical
interferometry regarding the surface of the magnetic layer before
performing the vacuum heating with respect to the magnetic tape is
3.0 nm to 7.0 nm.
5. The magnetic tape according to claim 1, wherein the full width
at half maximum of spacing distribution measured by optical
interferometry regarding the surface of the magnetic layer after
performing the vacuum heating with respect to the magnetic tape is
3.0 nm to 7.0 nm.
6. The magnetic tape according to claim 1, wherein the difference
S.sub.after-S.sub.before is 2.0 nm to 8.0 nm.
7. The magnetic tape according to claim 1, wherein a BET specific
surface area of the abrasive is 14 to 40 m.sup.2/g.
8. The magnetic tape according to claim 1, wherein the abrasive is
alumina powder.
9. The magnetic tape according to claim 1, wherein the magnetic
layer includes an aromatic hydrocarbon compound including a
phenolic hydroxyl group.
10. The magnetic tape according to claim 1, wherein the
ferromagnetic powder is ferromagnetic hexagonal ferrite powder.
11. The magnetic tape according to claim 10, wherein the
ferromagnetic hexagonal ferrite powder includes Al.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority under 35 U.S.C 119 to
Japanese Patent Application No. 2017-065751 filed on Mar. 29, 2017.
The above application is hereby expressly incorporated by
reference, in its entirety, into the present application.
BACKGROUND OF THE INVENTION
1. Field of the Invention
[0002] The present invention relates to a magnetic tape.
2. Description of the Related Art
[0003] Magnetic recording media are divided into tape-shaped
magnetic recording media and disk-shaped magnetic recording media,
and tape-shaped magnetic recording media, that is, magnetic tapes
are mainly used for data storage such as data back-up. The
recording and/or reproducing of information to the magnetic tape
are normally performed by mounting a magnetic tape cartridge
including the magnetic tape on a drive, allowing the magnetic tape
to run in the drive, and bringing the surface of the magnetic tape
(surface of a magnetic layer) to come into contact with a magnetic
head to slide thereon. Hereinafter, the magnetic tape is simply
referred to as a "tape" and the magnetic head is also simply
referred to as a "head".
[0004] For example, in order to continuously or intermittently
repeatedly reproduce the information recorded on the magnetic tape,
repeated running of the magnetic tape is performed in the drive
(hereinafter, also simply referred to as "repeated running"). It is
desired that a deterioration of electromagnetic conversion
characteristics during such repeated running is prevented, from a
viewpoint of increasing reliability of the magnetic tape for data
storage use. This is because a magnetic tape, in which
electromagnetic conversion characteristics during the repeated
running are hardly deteriorated, can continuously exhibit excellent
electromagnetic conversion characteristics, even in a case where
the running is continuously or intermittently repeated in a
drive.
[0005] As a reason of a deterioration of electromagnetic conversion
characteristics due to the repeated running, occurrence of a
phenomenon (called a "spacing loss") in which a distance between a
surface of a magnetic layer and a head is widened, is exemplified.
As a reason of this spacing loss, attachment of foreign materials
derived from a tape to a head, while a surface of a magnetic layer
and a head continue the sliding during the repeated running, that
is, generation of head attached materials is exemplified. In the
related art, as a measure against the generation of the head
attached materials, an abrasive has been included in the magnetic
layer, in order to impart a function of removing the head attached
materials to the surface of the magnetic layer (for example, see
JP2014-179149A). Hereinafter, the function of the surface of the
magnetic layer of removing the head attached materials is referred
to as "abrasion properties of the surface of the magnetic layer" or
simply "abrasion properties".
SUMMARY OF THE INVENTION
[0006] JP2014-179149A discloses that a magnetic tape disclosed in
JP2014-179149A can exhibit excellent electromagnetic conversion
characteristics. In order to increase reliability of such a
magnetic tape capable of exhibiting excellent electromagnetic
conversion characteristics, for use of data storage, it is desired
that a deterioration of electromagnetic conversion characteristics
during the repeated running is prevented. Therefore, the inventors
have made intensive research in order to find means for preventing
a deterioration of electromagnetic conversion characteristics
during the repeated running of the magnetic tape. From such
research, the inventors have focused that, not only generation of
head attached materials is a reason of spacing loss, but also
partial chipping of a head can be a reason of spacing loss.
Specific description is as follows. By increasing abrasion
properties of a surface of a magnetic layer, the spacing loss
caused by the head attached materials can be reduced. However, as
abrasion properties of the surface of the magnetic layer increase,
the head easily partially chips due to the sliding between the
surface of the magnetic layer and the head. In a case where partial
chipping of the head occurs, a distance between the surface of the
magnetic layer and the head in the chipped portion is widened. This
may also be a reason of the spacing loss.
[0007] In regards to abrasion properties of the surface of the
magnetic layer, as disclosed in JP2014-179149A, as an abrasive is
present in the magnetic layer in a fine state, abrasion properties
tend to be deteriorated. The partial chipping of the head can be
prevented by the deterioration of the abrasion properties, but the
head attached materials are hardly removed. As described above, a
decrease in the amount of the head attached materials and the
partial chipping of the head are in a relationship of the
tradeoff.
[0008] Meanwhile, in order to increase recording capacity for 1
reel of a magnetic tape cartridge, it is desired to increase the
total length of the magnetic tape accommodated in 1 reel of the
magnetic tape cartridge by decreasing the total thickness of the
magnetic tape (that is, thinning the magnetic tape). As one method
of thinning the magnetic tape, a method of decreasing the total
thickness of a non-magnetic layer and a magnetic layer of a
magnetic tape including the non-magnetic layer and the magnetic
layer on a non-magnetic support in this order is used. However, in
such studies of the inventor, it was clear that, it was difficult
to overcome the relationship of the tradeoff to prevent a
deterioration of electromagnetic conversion characteristics during
the repeated running in a low temperature and high humidity
environment, in a magnetic tape having a decreased total thickness
of a non-magnetic layer and a magnetic layer which is equal to or
smaller than 0.60 .mu.m, compared to a magnetic tape having the
total thickness of a non-magnetic layer and a magnetic layer which
exceeds 0.60 .mu.m. Hereinafter, the deterioration of
electromagnetic conversion characteristics indicates a
deterioration of electromagnetic conversion characteristics in a
low temperature and high humidity environment, unless otherwise
noted. The low temperature and high humidity environment can be,
for example, an environment in which an atmosphere temperature is
10.degree. C. to 20.degree. C. and a relative humidity is 70% to
90%. The magnetic tape may also be used in the low temperature and
high humidity environment, and therefore, it is desired that a
deterioration of electromagnetic conversion characteristics during
the repeated running is prevented in such an environment.
[0009] Therefore, an object of the invention is to provide a
magnetic tape which has the total thickness of a non-magnetic layer
and a magnetic layer equal to or smaller than 0.60 .mu.m and in
which electromagnetic conversion characteristics are hardly
deteriorated, even in a case where the running is repeated in a low
temperature and high humidity environment.
[0010] According to one aspect of the invention, there is provided
a magnetic tape comprising: a non-magnetic support; a non-magnetic
layer including non-magnetic powder and a binding agent on the
non-magnetic support; and a magnetic layer including ferromagnetic
powder and a binding agent on the non-magnetic layer, in which a
total thickness of the non-magnetic layer and the magnetic layer is
equal to or smaller than 0.60 .mu.m, the magnetic layer includes an
abrasive and fatty acid ester, a percentage of a plan view maximum
area of the abrasive confirmed in a region having a size of 4.3
.mu.m.times.6.3 .mu.m of a surface of the magnetic layer with
respect to the total area of the region, obtained by plane
observation performed by using a scanning electron microscope is
equal to or greater than 0.02% and less than 0.06%, a full width at
half maximum of spacing distribution measured by optical
interferometry regarding the surface of the magnetic layer before
performing a vacuum heating with respect to the magnetic tape is
greater than 0 nm and equal to or smaller than 7.0 nm, a full width
at half maximum of spacing distribution measured by optical
interferometry regarding the surface of the magnetic layer after
performing the vacuum heating with respect to the magnetic tape is
greater than 0 nm and equal to or smaller than 7.0 nm, and a
difference (S.sub.after-S.sub.before) between a spacing S.sub.after
measured by optical interferometry regarding the surface of the
magnetic layer after performing the vacuum heating with respect to
the magnetic tape and a spacing S.sub.before measured by optical
interferometry regarding the surface of the magnetic layer before
performing the vacuum heating with respect to the magnetic tape is
greater than 0 nm and equal to or smaller than 8.0 nm.
[0011] The magnetic tape includes an abrasive in the magnetic
layer. The abrasive is present in the magnetic layer in a state
where a percentage of a plan view maximum area of the abrasive
confirmed in a region having a size of 4.3 .mu.m.times.6.3 .mu.m of
the surface of the magnetic layer by plane observation using a
scanning electron microscope (SEM), with respect to the total area
(100%) of the region is equal to or greater than 0.02% and less
than 0.06%. Details of a measurement method of the percentage of
the plan view maximum area of the abrasive with respect to the
total area of the region (hereinafter, also referred to as a "plan
view maximum area percentage of the abrasive" or simply a
"percentage") will be described later.
[0012] Hereinafter, the full width at half maximum (FWHM) of
spacing distribution measured by optical interferometry regarding
the surface of the magnetic layer before performing the vacuum
heating with respect to the magnetic tape is also referred to as
"FWHM.sub.before" and the full width at half maximum of spacing
distribution measured by optical interferometry regarding the
surface of the magnetic layer after performing the vacuum heating
with respect to the magnetic tape is also referred to as
"FWHM.sub.after". The difference between a spacing S.sub.after
measured by optical interferometry regarding the surface of the
magnetic layer after performing the vacuum heating with respect to
the magnetic tape and a spacing S.sub.before measured by optical
interferometry regarding the surface of the magnetic layer before
performing the vacuum heating with respect to the magnetic tape is
also referred to as a "difference (S.sub.after-S.sub.before)". The
FWHM.sub.after and the spacing S.sub.after for acquiring the
difference (S.sub.after-S.sub.before) are values acquired after
performing the vacuum heating with respect to the magnetic tape. In
the invention and the specification, the "vacuum heating" of the
magnetic tape is performed by holding the magnetic tape in an
environment of a pressure of 200 Pa to 0.01 MPa and at an
atmosphere temperature of 70.degree. C. to 90.degree. C. for 24
hours.
[0013] In the invention and the specification, the spacing measured
by optical interferometry regarding the surface of the magnetic
layer of the magnetic tape is a value measured by the following
method.
[0014] In a state where the magnetic tape and a transparent
plate-shaped member (for example, glass plate or the like) are
overlapped with each other so that the surface of the magnetic
layer of the magnetic tape faces the transparent plate-shaped
member, a pressing member is pressed against the side of the
magnetic tape opposite to the magnetic layer side at a pressure of
5.05.times.10.sup.4 N/m (0.5 atm). In this state, the surface of
the magnetic layer of the magnetic tape is irradiated with light
through the transparent plate-shaped member (irradiation region:
150,000 to 200,000 .mu.m.sup.2), and a spacing (distance) between
the surface of the magnetic layer of the magnetic tape and the
surface of the transparent plate-shaped member on the magnetic tape
side is acquired based on intensity (for example, contrast of
interference fringe image) of interference light generated due to a
difference in a light path between reflected light from the surface
of the magnetic layer of the magnetic tape and reflected light from
the surface of the transparent plate-shaped member on the magnetic
tape side. The light emitted here is not particularly limited. In a
case where the emitted light is light having an emission wavelength
over a comparatively wide wavelength range as white light including
light having a plurality of wavelengths, a member having a function
of selectively cutting light having a specific wavelength or a
wavelength other than wavelengths in a specific wavelength range,
such as an interference filter, is disposed between the transparent
plate-shaped member and a light reception unit which receives
reflected light, and light at some wavelengths or in some
wavelength ranges of the reflected light is selectively incident to
the light reception unit. In a case where the light emitted is
light (so-called monochromatic light) having a single luminescence
peak, the member described above may not be used. The wavelength of
light incident to the light reception unit can be set to be 500 to
700 nm, for example. However, the wavelength of light incident to
the light reception unit is not limited to be in the range
described above. In addition, the transparent plate-shaped member
may be a member having transparency through which emitted light
passes, to the extent that the magnetic tape is irradiated with
light through this member and interference light is obtained.
[0015] The measurement described above can be performed by using a
commercially available tape spacing analyzer (TSA) such as Tape
Spacing Analyzer manufactured by Micro Physics, Inc., for example.
The spacing measurement of the examples was performed by using Tape
Spacing Analyzer manufactured by Micro Physics, Inc.
[0016] In addition, the full width at half maximum of spacing
distribution of the invention and the specification is a full width
at half maximum (FWHM), in a case where the interference fringe
image obtained by the measurement of the spacing described above is
divided into 300,000 points, a spacing of each point (distance
between the surface of the magnetic layer of the magnetic tape and
the surface of the transparent plate-shaped member on the magnetic
tape side) is acquired, this spacing is shown with a histogram, and
this histogram is fit with Gaussian distribution.
[0017] Further, the difference (S.sub.after-S.sub.before) is a
value obtained by subtracting a mode before the vacuum heating from
a mode after the vacuum heating of the 300,000 points.
[0018] In one aspect, the percentage of a plan view maximum area of
the abrasive confirmed in a region having a size of 4.3
.mu.m.times.6.3 .mu.m of the surface of the magnetic layer with
respect to the total area of the region, obtained by plane
observation performed by using a scanning electron microscope is
0.02% to 0.05%.
[0019] In one aspect, the total thickness of the non-magnetic layer
and the magnetic layer is 0.20 .mu.m to 0.60 .mu.m.
[0020] In one aspect, the FWHM.sub.before is 3.0 nm to 7.0 nm.
[0021] In one aspect, the FWHM.sub.after is 3.0 nm to 7.0 nm.
[0022] In one aspect, the difference (S.sub.after-S.sub.before) is
2.0 nm to 8.0 nm.
[0023] In one aspect, a Brunauer-Emmett-Teller (BET) specific
surface area of the abrasive is 14 to 40 m.sup.2/g.
[0024] In one aspect, the abrasive is alumina powder.
[0025] In one aspect, the magnetic layer includes an aromatic
hydrocarbon compound including a phenolic hydroxyl group.
[0026] In one aspect, ferromagnetic powder is ferromagnetic
hexagonal ferrite powder.
[0027] In one aspect, the ferromagnetic hexagonal ferrite powder
includes Al.
[0028] According to one aspect of the invention, it is possible to
provide a magnetic tape which has the total thickness of a
non-magnetic layer and a magnetic layer equal to or smaller than
0.60 .mu.m and in which electromagnetic conversion characteristics
during the repeated running are hardly deteriorated in a low
temperature and high humidity environment.
BRIEF DESCRIPTION OF THE DRAWING
[0029] FIG. 1 is a schematic configuration diagram of a vibration
imparting device used in examples.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0030] According to one aspect of the invention, there is provided
a magnetic tape including: a non-magnetic support; a non-magnetic
layer including non-magnetic powder and a binding agent on the
non-magnetic support; and a magnetic layer including ferromagnetic
powder and a binding agent on the non-magnetic layer, in which the
total thickness of the non-magnetic layer and the magnetic layer is
equal to or smaller than 0.60 .mu.m, the magnetic layer includes an
abrasive and fatty acid ester, a percentage of a plan view maximum
area of the abrasive confirmed in a region having a size of 4.3
.mu.m.times.6.3 .mu.m of the surface of the magnetic layer with
respect to the total area of the region, obtained by plane
observation performed by using a scanning electron microscope is
equal to or greater than 0.02% and less than 0.06%, a full width at
half maximum of spacing distribution measured by optical
interferometry regarding the surface of the magnetic layer before
performing a vacuum heating with respect to the magnetic tape
(FWHM.sub.before) is greater than 0 nm and equal to or smaller than
7.0 nm, a full width at half maximum of spacing distribution
measured by optical interferometry regarding the surface of the
magnetic layer after performing the vacuum heating with respect to
the magnetic tape (FWHM.sub.after) is greater than 0 nm and equal
to or smaller than 7.0 nm, and a difference
(S.sub.after-S.sub.before) between a spacing S.sub.after measured
by optical interferometry regarding the surface of the magnetic
layer after performing the vacuum heating with respect to the
magnetic tape and a spacing S.sub.before measured by optical
interferometry regarding the surface of the magnetic layer before
performing the vacuum heating with respect to the magnetic tape is
greater than 0 nm and equal to or smaller than 8.0 nm.
[0031] The following description contains surmise of the inventor.
The invention is not limited by such surmise.
[0032] The surmise of the inventors regarding the magnetic tape is
as follows.
[0033] (1) As described above, it was clear that, it was difficult
to prevent a deterioration of electromagnetic conversion
characteristics during the repeated running in a low temperature
and high humidity environment, in a magnetic tape having a
decreased total thickness of a non-magnetic layer and a magnetic
layer which is equal to or smaller than 0.60 .mu.m, compared to a
magnetic tape having the total thickness of a non-magnetic layer
and a magnetic layer which exceeds 0.60 .mu.m. The reason thereof
may be a change of a contact state between the surface of the
magnetic layer and the head due to a decrease of only the total
thickness of the non-magnetic layer and the magnetic layer. Due to
such a change of the contact state, the inventors have surmised
that a phenomenon that the head easily partially chips due to the
abrasive present in the magnetic layer may be one of the reasons of
the spacing loss. In regards to this point, the inventors have
considered that a state of the abrasive present in the magnetic
layer which is in a state satisfying a percentage which will be
described later in detail, indicates that the abrasive is present
in the magnetic layer in a fine state. The inventors have surmised
that this contributes to the prevention of partial chipping of the
head during the repeated running.
[0034] (2) However, in a case where the abrasive is only simply
present in the magnetic layer in a fine state, abrasion properties
of the surface of the magnetic layer are deteriorated. That is, a
function of removing head attached materials by the surface of the
magnetic layer are deteriorated. In regards to this point, the
inventors have investigated for preventing occurrence of spacing
loss due to head attached materials, even in a case where the
abrasive is present in the magnetic layer in a fine state, by
preventing generation of foreign materials derived from the tape,
and as a result, the inventors have thought that the
FWHM.sub.before, the FWHM.sub.after, and the difference
(S.sub.after-S.sub.before) are respectively set to be in the ranges
described above. More details thereof will be described later.
[0035] The inventors have surmised that, as a result of reducing
the spacing loss by satisfying both of the prevention of partial
chipping of the head and a decrease in the amount of the head
attached materials as described above, it is possible to prevent a
deterioration of electromagnetic conversion characteristics during
the repeated running in the magnetic tape having a decreased total
thickness of the non-magnetic layer and the magnetic layer which is
equal to or smaller than 0.60 .mu.m.
[0036] However, the invention is not limited to the surmises
described above.
[0037] Hereinafter, the magnetic tape will be described more
specifically.
[0038] In the invention and the specification, the "surface of the
magnetic layer" is identical to the surface of the magnetic tape on
the magnetic layer side. In the invention and the specification,
the "ferromagnetic powder" means an aggregate of a plurality of
ferromagnetic particles. The "aggregate" not only includes an
aspect in which particles configuring the aggregate directly come
into contact with each other, but also includes an aspect in which
a binding agent, an additive, or the like is interposed between the
particles. The points described above are also applied to various
powder such as non-magnetic powder of the invention and the
specification, in the same manner. The term "particles" may be used
for describe powder.
[0039] Total Thickness of Non-Magnetic Layer and Magnetic Layer
[0040] The total thickness of the non-magnetic layer and the
magnetic layer of the magnetic tape is equal to or smaller than
0.60 .mu.m and preferably equal to or smaller than 0.50 .mu.m, from
a viewpoint of thinning the magnetic tape. In addition, the total
thickness of the non-magnetic layer and the magnetic layer is, for
example, equal to or greater than 0.10 .mu.m or equal to or greater
than 0.20 .mu.m.
[0041] Various thicknesses such as a thickness of the non-magnetic
layer and a thickness of the magnetic layer will be described later
in detail. The thicknesses of various layers of the magnetic tape
and the non-magnetic support can be acquired by a well-known film
thickness measurement method. As an example, a cross section of the
magnetic tape in a thickness direction is, for example, exposed by
a well-known method of ion beams or microtome, and the exposed
cross section is observed with a scanning electron microscope. In
the cross section observation, various thicknesses can be acquired
as a thickness acquired at one position of the cross section in the
thickness direction, or an arithmetical mean of thicknesses
acquired at a plurality of positions of two or more positions, for
example, two positions which are arbitrarily extracted. In
addition, the thickness of each layer may be acquired as a designed
thickness calculated according to the manufacturing conditions.
[0042] State of Abrasive Present in Magnetic Layer
[0043] The magnetic tape includes an abrasive in the magnetic
layer. The abrasive is present in the magnetic layer in a state
where a percentage of a plan view maximum area of the abrasive
confirmed in a region having a size of 4.3 .mu.m.times.6.3 .mu.m of
the surface of the magnetic layer by plane observation performed
using a scanning electron microscope (SEM), with respect to the
total area (100%) of the region is equal to or greater than 0.02%
and less than 0.06%. The inventors have surmised that the abrasive
present in the magnetic layer in a state where the percentage is
equal to or greater than 0.02% contributes to the removal of the
head attached materials, and the abrasive present in the magnetic
layer in a state where the percentage is less than 0.06%
contributes to the prevention of partial chipping of the head.
Accordingly, the inventors have surmised that, the prevention of
occurrence of spacing loss contributes to the prevention of a
deterioration of electromagnetic conversion characteristics during
the repeated running in a low temperature and high humidity
environment. The percentage is preferably 0.02% to 0.05% and more
preferably 0.02% to 0.04%.
[0044] In the magnetic tape having the total thickness of the
non-magnetic layer and the magnetic layer equal to or smaller than
0.60 .mu.m, in addition to allowing the abrasive to be present in
the magnetic layer in a state where the percentage is equal to or
greater than 0.02% and less than 0.06%, setting the
FWHM.sub.before, the FWHM.sub.after, and the difference
(S.sub.after-S.sub.before) respectively to be in the ranges
described above contribute to the prevention of a deterioration of
electromagnetic conversion characteristics during the repeated
running in a low temperature and high humidity environment. This
point will be described later in detail.
[0045] Measurement Method
[0046] The plan view maximum area of the abrasive described above
is acquired by plane observation performed by using a scanning
electron microscope. As the scanning electron microscope, a field
emission (FE) type scanning electron microscope (FE-SEM) is used. A
scanning electron microscope image (SEM image) obtained by
plane-observing and imaging the surface of the magnetic layer from
the top by using the FE-SEM under the conditions of an acceleration
voltage of 5 kV, a working distance (W.D.) of 8 mm, and a
magnification ratio of imaging of 20,000 times, is analyzed and
accordingly, the plan view maximum area of the abrasive is
acquired. The percentage is calculated from the acquired plan view
maximum area. Specific procedure is as follows.
[0047] 1. Acquiring of SEM Image
[0048] An acceleration voltage is set as 5 kV, a working distance
(W.D.) is set as 8 mm, and a magnification ratio of imaging is set
as 20,000 times, and a SEM image is acquired as a secondary
electron image, without performing a sample coating before the
imaging. As the scanning electron microscope (FE-SEM), FE-SEM S4800
manufactured by Hitachi, Ltd. can be used, for example. Values of
Examples and Comparative Examples which will be described later are
values obtained by using FE-SEM S4800 manufactured by Hitachi, Ltd.
as the FE-SEM and setting a probe current as Normal.
[0049] 2. Image Analysis
[0050] The image analysis of the SEM image acquired in the section
1. is performed by the following procedure by using WinROOF
manufactured by Mitani Corporation as image analysis software. An
area of each portion described below is acquired as a value using a
pixel as a unit.
[0051] (1) The image data (SEM (20K) jpg image) of the SEM image
acquired in the section 1. is dragged-and-dropped in WinROOF.
[0052] (2) A region having a size of 4.3 .mu.m.times.6.3 .mu.m of
the image excluding a part where a magnification and a scale are
displayed, is selected as an analysis region.
[0053] (3) The image in the analysis region is subjected to
binarization processing. Specifically, 150 gradation is selected as
a lower limit value, 255 gradation is selected as an upper limit
value, and the binarization processing is performed by setting the
lower limit value and the upper limit value as threshold
values.
[0054] (4) By performing the binarization processing, an area of
each white shining portion of the analysis region is acquired.
Specifically, a command of measurement.fwdarw.shape
characteristics.fwdarw.area is executed in the image analysis
software WinROOF.
[0055] (5) The total area (4.3 .mu.m.times.6.3 .mu.m) of the
analysis region is set as 100%, a percentage of the area of each
portion acquired in (4) with respect to the total area is
calculated, and a maximum value of the percentage of the area of
each portion is acquired.
[0056] (6) The procedure of (2) to (5) is executed four times by
changing the position of the analysis region (N=4).
[0057] (7) An arithmetical mean (that is, arithmetical mean of four
maximum values) of the maximum values respectively acquired in (5)
during the execution of the procedure four times is calculated, and
the calculated value is set as the plan view maximum area of the
abrasive. A percentage of the plan view maximum area acquired as
described above occupying the total area of the analysis region is
calculated and the calculated percentage is set as the plan view
maximum area percentage of the abrasive.
[0058] Adjustment Method
[0059] By allowing the abrasive to be present in the magnetic layer
in a fine state, it is possible to realize a state where the
abrasive is present in the magnetic layer in a state where the
percentage is equal to or greater than 0.02% and less than 0.06%.
In order to allow the abrasive to be present in the magnetic layer
in a fine state, it is preferable that an abrasive having a small
particle size is used, the aggregate of the abrasive is prevented
and the abrasive is dispersed in the magnetic layer without being
unevenly distributed. As one method thereof, a method of
reinforcing the dispersion conditions of the abrasive at the time
of preparing a magnetic layer forming composition is used. For
example, separate dispersing the abrasive and the ferromagnetic
powder is one aspect of the reinforcement of the dispersion
conditions. The separate dispersing is more specifically a method
of preparing a magnetic layer forming composition through a step of
mixing an abrasive liquid including an abrasive and a solvent
(here, substantially not including ferromagnetic powder) with a
magnetic solution including the ferromagnetic powder, a solvent,
and a binding agent. By performing the mixing after separately
dispersing the abrasive and the ferromagnetic powder as described
above, it is possible to increase dispersibility of the abrasive of
the magnetic layer forming composition. The expression of
"substantially not including ferromagnetic powder" means that the
ferromagnetic powder is not added as a constituent component of the
abrasive liquid, and a small amount of the ferromagnetic powder
present as impurities being mixed without intention is allowed. By
arbitrarily combining methods such as use of dispersion media
having a small size (for example, decreasing a diameter of
dispersion beads in beads dispersion), a high degree of filling of
dispersion media of a dispersion device, and a dispersing process
performed for a long time, other than the separate dispersing or in
addition to the separate dispersing, it is possible to reinforce
the dispersion conditions. In a case of performing the filtering by
using a filter in the preparation of the magnetic layer forming
composition, a filter having a small hole diameter tends to cause
the abrasive to be present in the magnetic layer in a fine
state.
[0060] Dispersing Agent
[0061] In addition, the use of a dispersing agent for improving
dispersibility of the abrasive can also be one aspect of the
reinforcement of the dispersion conditions of the abrasive. Here,
the dispersing agent for improving dispersibility of the abrasive
is a component which can increase dispersibility of the abrasive in
the magnetic layer forming composition and/or the abrasive liquid,
compared to a state where this agent is not present. As a compound
which can function as such a dispersing agent, an aromatic
hydrocarbon compound including a phenolic hydroxyl group can be
used. The "phenolic hydroxyl group" is a hydroxyl group directly
combined with an aromatic ring. The aromatic ring included in the
aromatic hydrocarbon compound may have a monocyclic or polycyclic
structure, or may a fused ring. From a viewpoint of improving
dispersibility of the abrasive, an aromatic hydrocarbon compound
including a benzene ring or a naphthalene ring is preferable. In
addition, the aromatic hydrocarbon compound may include a
substituent other than the phenolic hydroxyl group. Examples of the
substituent other than the phenolic hydroxyl group include a
halogen atom, an alkyl group, an alkoxy group, an amino group, an
acyl group, a nitro group, a nitroso group, and a hydroxyalkyl
group, and a halogen atom, an alkyl group, an alkoxy group, an
amino group, and a hydroxyalkyl group are preferable. The phenolic
hydroxyl group included in one molecule of the aromatic hydrocarbon
compound may be 1, 2, 3, or more.
[0062] As one preferable aspect of the aromatic hydrocarbon
compound including a phenolic hydroxyl group, a compound
represented by General Formula 100.
##STR00001##
[0063] [In General Formula 100, two of X.sup.101 to X.sup.108 are
hydroxyl groups and other six components each independently
represent a hydrogen atom or a substituent.
[0064] In the compound represented by General Formula 100, a site
of substitution of the two hydroxyl groups (phenolic hydroxyl
groups) is not particularly limited.
[0065] In the compound represented by General Formula 100, two of
X.sup.101 to X.sup.108 are hydroxyl groups (phenolic hydroxyl
groups) and other six components each independently represent a
hydrogen atom or a substituent. In addition, among X.sup.101 to
X.sup.108, all of portions other than the two hydroxyl groups may
be hydrogen atoms or some or all of the portions may be
substituents. As the substituent, the substituents described above
can be used. As the substituent other than the two hydroxyl groups,
one or more phenolic hydroxyl groups may be included. From a
viewpoint of improving dispersibility of the abrasive, it is
preferable that the components other than the two hydroxyl groups
among X.sup.101 to X.sup.108 are not phenolic hydroxyl groups. That
is, the compound represented by General Formula 100 is preferably
dihydroxynaphthalene or a derivative thereof and more preferably
2,3-dihydroxynaphthalene or a derivative thereof. Examples of a
preferable substituent as the substituent represented by X.sup.101
to X.sup.108 include a halogen atom (for example, a chlorine atom,
a bromine atom), an amino group, an alkyl group having 1 to 6
(preferably 1 to 4) carbon atoms, a methoxy group and an ethoxy
group, an acyl group, a nitro group, a nitroso group, and a
--CH.sub.2OH group.
[0066] As the dispersing agent for improving dispersibility of the
abrasive, descriptions disclosed in paragraphs 0024 to 0028 of
JP2014-179149A can be referred to.
[0067] The content of the dispersing agent for improving
dispersibility of the abrasive described above can be used, for
example, 0.5 to 20.0 parts by mass and is preferably 1.0 to 10.0
parts by mass with respect to 100.0 parts by mass of the abrasive,
at the time of preparing the magnetic layer forming composition,
preferably at the time of preparing the abrasive liquid.
[0068] Abrasive
[0069] The "abrasive" means non-magnetic powder having Mohs
hardness exceeding 8 and is preferably non-magnetic powder having
Mohs hardness equal to or greater than 9. The abrasive may be
powder of inorganic substances (inorganic powder) or may be powder
of organic substances (organic powder). The abrasive is more
preferably inorganic powder having Mohs hardness exceeding 8 and
even more preferably inorganic powder having Mohs hardness equal to
or greater than 9. A maximum value of Mohs hardness is 10 of
diamond. Specifically, powders of alumina (Al.sub.2O.sub.3),
silicon carbide, boron carbide (B.sub.4C), TiC, cerium oxide,
zirconium oxide (ZrO.sub.2), diamond, and the like can be used as
the abrasive, and among these, alumina powder is preferable. The
aromatic hydrocarbon compound including a phenolic hydroxyl group
described above is particularly preferably used as a dispersing
agent for improving dispersibility of alumina powder. There are
mainly two kinds of alumina having an alpha type crystal form and a
gamma type crystal form. Both can be used, it is preferable to use
alumina (.alpha.-alumina) having an alpha type crystal form, from
viewpoints of realizing higher hardness and contributing to the
improvement of abrasion properties and the improvement of the
strength of the magnetic layer. A gelatinization ratio of
.alpha.-alumina is preferably equal to or greater than 50% from a
viewpoint of hardness. The shape of the particles of the abrasive
may be any shape of an acicular shape, a spherical shape, and a
dice shape.
[0070] In order to obtain a magnetic layer in which the abrasive is
present in a fine state, it is preferable to use an abrasive having
a small particle size as the abrasive. As an index of the particle
size of the abrasive, a BET specific surface area can be used. A
large BET specific surface area means a small particle size. From a
viewpoint of a small particle size, the BET specific surface area
of the abrasive is preferably equal to or greater than 14
m.sup.2/g, more preferably equal to or greater than 15 m.sup.2/g,
even more preferably equal to or greater than 18 m.sup.2/g, and
still more preferably 20 m.sup.2/g. In addition, from a viewpoint
of ease of improvement of dispersibility, an abrasive having a BET
specific surface area equal to or smaller than 40 m.sup.2/g is
preferably used.
[0071] A preparing method of the magnetic layer forming composition
including the abrasive will be described later in detail.
[0072] Difference (S.sub.after-S.sub.before)
[0073] The difference (S.sub.after-S.sub.before) of the spacings
before and after the vacuum heating measured in the magnetic tape
is greater than 0 nm and equal to or smaller than 8.0 nm. Regarding
the difference (S.sub.after-S.sub.before), the inventors have
thought that this value can be an index for a thickness of a liquid
film formed on the surface of the magnetic layer with fatty acid
ester included in the magnetic layer. Specific description is as
follows.
[0074] A portion (projection) which mainly comes into contact
(so-called real contact) with the head in a case where the magnetic
tape and the head slide on each other, and a portion (hereinafter,
referred to as a "base portion") having a height lower than that of
the portion described above are normally present on the surface of
the magnetic layer. The inventors have thought that the spacing
described above is a value which is an index of a distance between
the head and the base portion in a case where the magnetic tape and
the head slide on each other. However, it is thought that, in a
case where fatty acid ester included in the magnetic layer forms a
liquid film on the surface of the magnetic layer, the liquid film
is present between the base portion and the head, and thus, the
spacing is narrowed by the thickness of the liquid film.
[0075] Meanwhile, the lubricant is generally divided broadly into a
liquid lubricant and a boundary lubricant and fatty acid ester is
known as a component which can function as a liquid lubricant. It
is considered that fatty acid ester can protect the magnetic layer
by forming a liquid film on the surface of the magnetic layer. The
inventors have thought that the protection of the surface of the
magnetic layer due to the presence of the liquid film of fatty acid
ester contributes to preventing the surface of the magnetic layer
from chipping due to the sliding on the head, and preventing cut
scraps from becoming head attached materials. However, it is
thought that an excessive amount of fatty acid ester present on the
surface of the magnetic layer causes sticking due to strong
adhesiveness due to formation of a meniscus (liquid crosslinking)
between the surface of the magnetic layer and the head due to fatty
acid ester.
[0076] In regards to this point, the inventors focused on the idea
that fatty acid ester is a component having properties of
volatilizing by vacuum heating, and the difference
(S.sub.after-S.sub.before) of a spacing between a state after the
vacuum heating (state in which a liquid film of fatty acid ester is
volatilized and removed) and a state before the vacuum heating
(state in which the liquid film of fatty acid ester is present) was
used as an index for the thickness of the liquid film formed of
fatty acid ester on the surface of the magnetic layer. The
inventors have surmised that the presence of the liquid film of
fatty acid ester on the surface of the magnetic layer, so that the
value of the difference is greater than 0 nm and equal to or
smaller than 8.0 nm, prevents generation of cut scraps due to
chipping of the surface of the magnetic layer due to sliding on the
head, while preventing sticking. From a viewpoint of further
preventing chipping of the surface of the magnetic layer, the
difference (S.sub.after-S.sub.before) is preferably equal to or
greater than 0.1 nm, more preferably equal to or greater than 1.0
nm, even more preferably equal to or greater than 1.5 nm, still
preferably equal to or greater than 2.0 nm, still more preferably
equal to or greater than 2.5 nm, still furthermore preferably equal
to or greater than 3.0 nm. Meanwhile, from a viewpoint of further
preventing occurrence of sticking, the difference
(S.sub.after-S.sub.before) is preferably equal to or smaller than
7.5 nm, more preferably equal to or smaller than 7.0 nm, even more
preferably equal to or smaller than 6.5 nm, still preferably equal
to or smaller than 6.0 nm, still more preferably equal to or
smaller than 5.0 nm, still even more preferably equal to or smaller
than 4.5 nm, and still even furthermore preferably equal to or
smaller than 4.0 nm. The difference (S.sub.after-S.sub.before) can
be controlled by the amount of fatty acid ester added to a magnetic
layer forming composition. In addition, regarding the magnetic tape
including a non-magnetic layer between the non-magnetic support and
the magnetic layer, the difference (S.sub.after-S.sub.before) can
be controlled by the amount of fatty acid ester added to a
non-magnetic layer forming composition. This is because that the
non-magnetic layer can play a role of holding a lubricant and
supplying the lubricant to the magnetic layer, and fatty acid ester
included in the non-magnetic layer may be moved to the magnetic
layer and present in the surface of the magnetic layer.
[0077] FWHM.sub.before and FWHM.sub.after
[0078] A smaller value of the full width at half maximum of spacing
distribution means that a variation in the values of the spacing
measured on each part of the surface of the magnetic layer is
small. As a result of intensive studies, the inventors have thought
that, in order to prevent sticking between the surface of the
magnetic layer of the magnetic tape and the head and occurrence of
chipping of the surface of the magnetic layer during the running,
it is effective to increase uniformity of a contact state between
the surface of the magnetic layer and the head, by increasing
uniformity of a height of projections present on the surface of the
magnetic layer and increasing uniformity of a thickness of a liquid
film of fatty acid ester. The inventors have thought that an
increase in uniformity of the contact state between the surface of
the magnetic layer and the head is also effective to improvement of
electromagnetic conversion characteristics, because a decrease in
electromagnetic conversion characteristics due to spacing variation
is prevented.
[0079] In regards to this point, it is considered that the reason
for the variation in values of the spacing is a variation in height
of the projection of the surface of the magnetic layer and a
variation in the thickness of the liquid film fatty acid ester. The
inventors have surmised that the full width at half maximum of the
spacing distribution FWHM.sub.before measured before the vacuum
heating, that is, in a state where the liquid film of fatty acid
ester is present on the surface of the magnetic layer, becomes
great, as the variation in height of the projection and the
variation in the thickness of the liquid film of fatty acid ester
are great. Particularly, the spacing distribution FWHM.sub.before
is greatly affected by the variation in the thickness of the liquid
film of fatty acid ester. In contrast, the inventors have surmised
that the full width at half maximum of the spacing distribution
FWHM.sub.after measured after the vacuum heating, that is, in a
state where the liquid film of fatty acid ester is removed from the
surface of the magnetic layer, becomes great, as the variation in
height of the projection is great. That is, the inventors have
surmised that small full widths at half maximum of spacing
distributions FWHM.sub.before and FWHM.sub.after mean a small
variation in the thickness of the liquid film of fatty acid ester
on the surface of the magnetic layer and a small variation in
height of the projection. The inventors have thought that it is
possible to prevent sticking between the surface of the magnetic
layer of the magnetic tape and the head and occurrence of chipping
of the surface of the magnetic layer during running, and improve
electromagnetic conversion characteristics, by increasing the
uniformity of the height of the projection and the thickness of the
liquid film of fatty acid ester so that the full widths at half
maximum of the spacing distributions FWHM.sub.before and
FWHM.sub.after are greater than 0 nm and equal to or smaller than
7.0 nm.
[0080] Both of the full width at half maximum of spacing
distribution FWHM.sub.before before the vacuum heating and the full
width at half maximum of spacing distribution FWHM.sub.after after
the vacuum heating which are measured in the magnetic tape are
greater than 0 nm and equal to or smaller than 7.0 nm. It is
thought that this point contributes to the prevention of sticking
of the surface of the magnetic layer of the magnetic tape and the
head and occurrence of chipping of the surface of the magnetic
layer during running. From a viewpoint of further preventing the
sticking and occurrence of chipping of the surface of the magnetic
layer, the FWHM.sub.before and the FWHM.sub.after are preferably
equal to or smaller than 6.5 nm, more preferably equal to or
smaller than 6.0 nm, even more preferably equal to or smaller than
5.5 nm, still more preferably equal to or smaller than 5.0 nm, and
still even more preferably equal to or smaller than 4.5 nm. The
FWHM.sub.before and the FWHM.sub.after can be, for example, equal
to or greater than 0.5 nm, equal to or greater than 1.0 nm, equal
to or greater than 2.0 nm, or equal to or greater than 3.0 nm.
Meanwhile, from a viewpoint of preventing the sticking and
occurrence of chipping of the surface of the magnetic layer, it
tends to be preferable that the values thereof are small, and
therefore, the values thereof may be smaller than the exemplified
values.
[0081] The FWHM.sub.before measured before the vacuum heating can
be decreased mainly by decreasing the variation in the thickness of
the liquid film of fatty acid ester. An example of a specific
method will be described later. Meanwhile, the FWHM.sub.after
measured after the vacuum heating can be decreased by decreasing
the variation in height of the projection of the surface of the
magnetic layer. In order to realize the decrease described above,
it is preferable that a presence state of the powder component
included in the magnetic layer, for example, non-magnetic filler,
which will be described later specifically, in the magnetic layer
is controlled. An example of a specific method will be described
later.
[0082] Next, the magnetic layer and the like of the magnetic tape
will be described more specifically.
[0083] Magnetic Layer
[0084] Ferromagnetic Powder
[0085] As the ferromagnetic powder included in the magnetic layer,
ferromagnetic powder normally used in the magnetic layer of various
magnetic recording media can be used. It is preferable to use
ferromagnetic powder having a small average particle size, from a
viewpoint of improvement of recording density of the magnetic tape.
From this viewpoint, ferromagnetic powder having an average
particle size equal to or smaller than 50 nm is preferably used as
the ferromagnetic powder. Meanwhile, the average particle size of
the ferromagnetic powder is preferably equal to or greater than 10
nm, from a viewpoint of stability of magnetization.
[0086] As a preferred specific example of the ferromagnetic powder,
ferromagnetic hexagonal ferrite powder can be used. An average
particle size of the ferromagnetic hexagonal ferrite powder is
preferably 10 nm to 50 nm and more preferably 20 nm to 50 nm, from
a viewpoint of improvement of recording density and stability of
magnetization.
[0087] As one aspect of the ferromagnetic hexagonal ferrite powder,
ferromagnetic hexagonal ferrite powder including Al can be used. It
is thought that, the ferromagnetic hexagonal ferrite powder is
hardened by including Al and contributes to the improvement of
strength of the magnetic layer. The Al content of the ferromagnetic
hexagonal ferrite powder is preferably equal to or greater than 0.6
mass %, more preferably equal to or greater than 1.0 mass %, even
more preferably equal to or greater than 2.0 mass %, and still more
preferably equal to or greater than 3.0 mass % in terms of
Al.sub.2O.sub.3, with respect to 100.0 mass % of the total mass of
the ferromagnetic hexagonal ferrite powder. In addition, the Al
content of the ferromagnetic hexagonal ferrite powder is preferably
equal to or smaller than 12.0 mass %, more preferably equal to or
smaller than 10.0 mass %, even more preferably equal to or smaller
than 8.0 mass %, and still more preferably equal to or smaller than
6.0 mass % in terms of Al.sub.2O.sub.3, with respect to 100.0 mass
% of the total mass of the ferromagnetic hexagonal ferrite
powder.
[0088] Al may be present in the particle of the ferromagnetic
hexagonal ferrite powder, may be adhered to the surface of the
particle, or may be present in the particle and on the surface
thereof.
[0089] The Al content of the ferromagnetic hexagonal ferrite powder
can be calculated from an Al/Fe ratio acquired by inductively
coupled plasma (ICP) analysis. In addition, the Al adhered to the
surface of the particle can be confirmed by one or more analysis
methods of: confirming that an Al/Fe ratio of a surface layer of a
particle acquired by X-ray photoelectron spectroscopy (XPS)
analysis becomes greater than the Al/Fe ratio acquired by the ICP
analysis; observing localization of Al on the surface layer of the
particle in Auger electron spectroscopy (AES) analysis; and
confirming a coated film on the surface of the particle in a cross
section observation performed by using a transmission electron
microscope (TEM). It is surmised that Al present on the surface of
the particle is normally in a state of an oxide.
[0090] For a preparation method of the ferromagnetic hexagonal
ferrite powder including Al, description disclosed in paragraphs
0012 to 0030 of JP2011-225417A can be referred to. According to the
preparation method disclosed in JP2011-225417A, the ferromagnetic
hexagonal ferrite powder in which surfaces of primary particles of
hexagonal ferrite particles are coated with Al can also be obtained
by a glass crystallization method. In addition, for the preparation
method of the ferromagnetic hexagonal ferrite powder including Al,
description disclosed in a paragraph 0035 of JP2014-179149A can
also be referred to.
[0091] For details of ferromagnetic hexagonal ferrite powder, for
example, descriptions disclosed in paragraphs 0134 0136 of
JP2011-216149A and paragraphs 0013 to 0030 of JP2012-204726A can be
referred to.
[0092] As a preferred specific example of the ferromagnetic powder,
ferromagnetic metal powder can also be used. An average particle
size of the ferromagnetic metal powder is preferably 10 nm to 50 nm
and more preferably 20 nm to 50 nm, from a viewpoint of improvement
of recording density and stability of magnetization. For details of
the ferromagnetic metal powder, descriptions disclosed in
paragraphs 0137 to 0141 of JP2011-216149A and paragraphs 0009 to
0023 of JP2005-251351 can be referred to, for example.
[0093] In the invention and the specification, average particle
sizes of various powder such as the ferromagnetic powder and the
like are values measured by the following method with a
transmission electron microscope, unless otherwise noted.
[0094] The powder is imaged at a magnification ratio of 100,000
with a transmission electron microscope, the image is printed on
printing paper so that the total magnification of 500,000 to obtain
an image of particles configuring the powder. A target particle is
selected from the obtained image of particles, an outline of the
particle is traced with a digitizer, and a size of the particle
(primary particle) is measured. The primary particle is an
independent particle which is not aggregated.
[0095] The measurement described above is performed regarding 500
particles arbitrarily extracted. An arithmetical mean of the
particle size of 500 particles obtained as described above is an
average particle size of the powder. As the transmission electron
microscope, a transmission electron microscope H-9000 manufactured
by Hitachi, Ltd. can be used, for example. In addition, the
measurement of the particle size can be performed by well-known
image analysis software, for example, image analysis software
KS-400 manufactured by Carl Zeiss. The average particle size shown
in examples which will be described later is a value measured by
using transmission electron microscope H-9000 manufactured by
Hitachi, Ltd. as the transmission electron microscope, and image
analysis software KS-400 manufactured by Carl Zeiss as the image
analysis software, unless otherwise noted.
[0096] As a method of collecting a sample powder from the magnetic
tape in order to measure the particle size, a method disclosed in a
paragraph of 0015 of JP2011-048878A can be used, for example.
[0097] In the invention and the specification, unless otherwise
noted, (1) in a case where the shape of the particle observed in
the particle image described above is a needle shape, a fusiform
shape, or a columnar shape (here, a height is greater than a
maximum long diameter of a bottom surface), the size (particle
size) of the particles configuring the powder is shown as a length
of a long axis configuring the particle, that is, a long axis
length, (2) in a case where the shape of the particle is a planar
shape or a columnar shape (here, a thickness or a height is smaller
than a maximum long diameter of a plate surface or a bottom
surface), the particle size is shown as a maximum long diameter of
the plate surface or the bottom surface, and (3) in a case where
the shape of the particle is a sphere shape, a polyhedron shape, or
an unspecified shape, and the long axis configuring the particles
cannot be specified from the shape, the particle size is shown as
an equivalent circle diameter. The equivalent circle diameter is a
value obtained by a circle projection method.
[0098] In addition, regarding an average acicular ratio of the
powder, a length of a short axis, that is, a short axis length of
the particles is measured in the measurement described above, a
value of (long axis length/short axis length) of each particle is
obtained, and an arithmetical mean of the values obtained regarding
500 particles is calculated. Here, unless otherwise noted, in a
case of (1), the short axis length as the definition of the
particle size is a length of a short axis configuring the particle,
in a case of (2), the short axis length is a thickness or a height,
and in a case of (3), the long axis and the short axis are not
distinguished, thus, the value of (long axis length/short axis
length) is assumed as 1, for convenience.
[0099] In addition, unless otherwise noted, in a case where the
shape of the particle is specified, for example, in a case of
definition of the particle size (1), the average particle size is
an average long axis length, in a case of the definition (2), the
average particle size is an average plate diameter, and an average
plate ratio is an arithmetical mean of (maximum long
diameter/thickness or height). In a case of the definition (3), the
average particle size is an average diameter (also referred to as
an average particle diameter).
[0100] The content (filling percentage) of the ferromagnetic powder
of the magnetic layer is preferably 50 to 90 mass % and more
preferably 60 to 90 mass %. The components other than the
ferromagnetic powder of the magnetic layer are a binding agent, an
abrasive, and fatty acid ester, and one or more kinds of additives
may be arbitrarily included. A high filling percentage of the
ferromagnetic powder in the magnetic layer is preferable from a
viewpoint of improvement recording density.
[0101] Binding Agent
[0102] The magnetic tape is a coating type magnetic tape, and the
magnetic layer includes a binding agent together with the
ferromagnetic powder and the abrasive. As the binding agent, one or
more kinds of resin is used. The resin may be a homopolymer or a
copolymer. As the binding agent, various resins normally used as a
binding agent of the coating type magnetic recording medium can be
used. For example, as the binding agent, a resin selected from a
polyurethane resin, a polyester resin, a polyamide resin, a vinyl
chloride resin, an acrylic resin obtained by copolymerizing
styrene, acrylonitrile, or methyl methacrylate, a cellulose resin
such as nitrocellulose, an epoxy resin, a phenoxy resin, and a
polyvinylalkylal resin such as polyvinyl acetal or polyvinyl
butyral can be used alone or a plurality of resins can be mixed
with each other to be used. Among these, a polyurethane resin, an
acrylic resin, a cellulose resin, and a vinyl chloride resin are
preferable. These resins can be used as the binding agent even in
the non-magnetic layer and/or a back coating layer which will be
described later. For the binding agent described above, description
disclosed in paragraphs 0028 to 0031 of JP2010-24113A can be
referred to. In addition, the binding agent may be a radiation
curable resin such as an electron beam-curable resin. For the
radiation curable resin, descriptions disclosed in paragraphs 0044
and 0045 of JP2011-048878A can be referred to.
[0103] An average molecular weight of the resin used as the binding
agent can be, for example, 10,000 to 200,000 as a weight-average
molecular weight. The weight-average molecular weight of the
invention and the specification is a value obtained by performing
polystyrene conversion of a value measured by gel permeation
chromatography (GPC). As the measurement conditions, the following
conditions can be used. The weight-average molecular weight shown
in examples which will be described later is a value obtained by
performing polystyrene conversion of a value measured under the
following measurement conditions.
[0104] GPC device: HLC-8120 (manufactured by Tosoh Corporation)
[0105] Column: TSK gel Multipore HXL-M (manufactured by Tosoh
Corporation, 7.8 mmID (inner diameter).times.30.0 cm)
[0106] Eluent: Tetrahydrofuran (THF)
[0107] In addition, a curing agent can also be used together with
the binding agent. As the curing agent, in one aspect, a
thermosetting compound which is a compound in which a curing
reaction (crosslinking reaction) proceeds due to heating can be
used, and in another aspect, a photocurable compound in which a
curing reaction (crosslinking reaction) proceeds due to light
irradiation can be used. At least a part of the curing agent is
included in the magnetic layer in a state of being reacted
(crosslinked) with other components such as the binding agent, by
proceeding the curing reaction in the magnetic layer forming step.
The preferred curing agent is a thermosetting compound,
polyisocyanate is suitable. For details of the polyisocyanate,
descriptions disclosed in paragraphs 0124 and 0125 of
JP2011-216149A can be referred to, for example. The amount of the
curing agent can be, for example, 0 to 80.0 parts by mass with
respect to 100.0 parts by mass of the binding agent in the magnetic
layer forming composition, and is preferably 50.0 to 80.0 parts by
mass, from a viewpoint of improvement of strength of each layer
such as the magnetic layer.
[0108] Fatty Acid Ester
[0109] The magnetic tape includes fatty acid ester in the magnetic
layer. The fatty acid ester may be included alone as one type or
two or more types thereof may be included. Examples of fatty acid
ester include esters of lauric acid, myristic acid, palmitic acid,
stearic acid, oleic acid, linoleic acid, linolenic acid, behenic
acid, erucic acid, and elaidic acid. Specific examples thereof
include butyl myristate, butyl palmitate, butyl stearate (butyl
stearate), neopentyl glycol dioleate, sorbitan monostearate,
sorbitan distearate, sorbitan tristearate, oleyl oleate, isocetyl
stearate, isotridecyl stearate, octyl stearate, isooctyl stearate,
amyl stearate, and butoxyethyl stearate.
[0110] The content of fatty acid ester, as the content of the
magnetic layer forming composition, is, for example, 0.1 to 10.0
parts by mass and is preferably 1.0 to 7.0 parts by mass with
respect to 100.0 parts by mass of ferromagnetic powder. In a case
of using two or more kinds of different fatty acid esters as the
fatty acid ester, the content thereof is the total content thereof.
In the invention and the specification, the same applies to content
of other components, unless otherwise noted. In addition, in the
invention and the specification, a given component may be used
alone or used in combination of two or more kinds thereof, unless
otherwise noted.
[0111] In a case where the magnetic tape includes a non-magnetic
layer between the non-magnetic support and the magnetic layer, the
content of fatty acid ester in a non-magnetic layer forming
composition is, for example, 0 to 10.0 parts by mass and is
preferably 0.1 to 8.0 parts by mass with respect to 100.0 parts by
mass of non-magnetic powder.
[0112] Other Lubricants
[0113] The magnetic tape includes fatty acid ester which is one
kind of lubricants at least in the magnetic layer. The lubricants
other than fatty acid ester may be arbitrarily included in the
magnetic layer and/or the non-magnetic layer. As described above,
the lubricant included in the non-magnetic layer may be moved to
the magnetic layer and present in the surface of the magnetic
layer. As the lubricant which may be arbitrarily included, fatty
acid can be used. In addition, fatty acid amide and the like can
also be used. Fatty acid ester is known as a component which can
function as a liquid lubricant, whereas fatty acid and fatty acid
amide are known as a component which can function as a boundary
lubricant. It is considered that the boundary lubricant is a
lubricant which can be adsorbed to a surface of powder (for
example, ferromagnetic powder) and form a rigid lubricant film to
decrease contact friction.
[0114] Examples of fatty acid include lauric acid, myristic acid,
palmitic acid, stearic acid, oleic acid, linoleic acid, linolenic
acid, behenic acid, erucic acid, and elaidic acid, and stearic
acid, myristic acid, and palmitic acid are preferable, and stearic
acid is more preferable. Fatty acid may be included in the magnetic
layer in a state of salt such as metal salt.
[0115] As fatty acid amide, amide of various fatty acid described
above is used, and examples thereof include lauric acid amide,
myristic acid amide, palmitic acid amide, and stearic acid
amide.
[0116] Regarding fatty acid and a derivative of fatty acid (amide
and ester), a part derived from fatty acid of the fatty acid
derivative preferably has a structure which is the same as or
similar to that of fatty acid used in combination. As an example,
in a case of using stearic acid as fatty acid, it is preferable to
use stearic acid ester and/or stearic acid amide.
[0117] The content of fatty acid in the magnetic layer forming
composition is, for example, 0 to 10.0 parts by mass, preferably
0.1 to 10.0 parts by mass, and more preferably 1.0 to 7.0 parts by
mass, with respect to 100.0 parts by mass of the ferromagnetic
powder. The content of fatty acid amide in the magnetic layer
forming composition is, for example, 0 to 3.0 parts by mass,
preferably 0 to 2.0 parts by mass, and more preferably 0 to 1.0
part by mass with respect to 100.0 parts by mass of the
ferromagnetic powder.
[0118] In a case where the magnetic tape includes a non-magnetic
layer between the non-magnetic support and the magnetic layer, the
content of fatty acid in the non-magnetic layer forming composition
is, for example, 0 to 10.0 parts by mass, preferably 1.0 to 10.0
parts by mass, and more preferably 1.0 to 7.0 parts by mass with
respect to 100.0 parts by mass of the non-magnetic powder. The
content of fatty acid amide in the non-magnetic layer forming
composition is, for example, 0 to 3.0 parts by mass and preferably
0 to 1.0 part by mass with respect to 100.0 parts by mass of the
non-magnetic powder.
[0119] Additives
[0120] The magnetic layer includes ferromagnetic powder, a binding
agent, an abrasive, and fatty acid ester, and may further include
one or more kinds of additives, if necessary. As the additives, a
commercially available product or an additive prepared by a
well-known method can be suitably selected and used according to
desired properties.
[0121] As specific examples of the additives, the dispersing agent,
the curing agent described above, and various lubricants are used.
The dispersing agent for improving dispersibility of the abrasive
can also contribute to improvement of dispersibility of
ferromagnetic powder. The dispersing agent for improving
dispersibility of the ferromagnetic powder can also contribute to
the improvement of dispersibility of the abrasive. In addition,
examples of the additive which can be included in the magnetic
layer include a non-magnetic filler, a dispersing assistant, an
antibacterial agent, an antistatic agent, and an antioxidant. The
non-magnetic filler is identical to the non-magnetic powder. As the
non-magnetic filler, a non-magnetic filler (hereinafter, referred
to as a "projection formation agent") which can function as a
projection formation agent which forms projections suitably
protruded from the surface of the magnetic layer can be used.
[0122] The projection formation agent may be powder of inorganic
substances (inorganic powder) or powder of organic substances
(organic powder), and is preferably powder of inorganic substances.
In addition, carbon black is also preferable. An average particle
size of carbon black is preferably equal to or greater than 20 nm
and more preferably equal to or greater than 30 nm. In addition,
the average particle size of carbon black is preferably equal to or
smaller than 150 nm and more preferably equal to or smaller than
100 nm.
[0123] Examples of the inorganic powder include powder of inorganic
oxide such as metal oxide, metal carbonate, metal sulfate, metal
nitride, metal carbide, and metal sulfide, and specific examples
thereof include powder of silicon oxide such as silicon dioxide,
chromium oxide, .alpha.-iron oxide, goethite, corundum, silicon
nitride, titanium dioxide, tin oxide, magnesium oxide, tungsten
oxide, boron nitride, zinc oxide, calcium carbonate, calcium
sulfate, barium sulfate, and molybdenum disulfide, or composite
inorganic powder including two or more kinds thereof. The inorganic
oxide powder is more preferable and silicon oxide powder is even
more preferable.
[0124] The projection formation agent preferably has uniformity of
the particle size, from a viewpoint of further improving
electromagnetic conversion characteristics. From a viewpoint of
availability of particles having high uniformity of the particle
size, the projection formation agent is preferably colloidal
particles. In the invention and the specification, the "colloidal
particles" are particles which are not precipitated and dispersed
to generate a colloidal dispersion, in a case where 1 g of the
particles is added to 100 mL of at least one organic solvent of at
least methyl ethyl ketone, cyclohexanone, toluene, or ethyl
acetate, or a mixed solvent including two or more kinds of the
solvent described above at an arbitrary mixing ratio. The average
particle size of the colloidal particles is a value obtained by a
method disclosed in a paragraph 0015 of JP2011-048878A as a
measurement method of an average particle diameter. In a case where
the non-magnetic filler used in the formation of the magnetic layer
is available, it is possible to determine whether or not the
non-magnetic filler included in the magnetic layer is colloidal
particles, by evaluating whether or not such a non-magnetic filler
has properties which are the properties of the colloidal particles
described above. Alternatively, the determination can also be
performed by evaluating whether or not the non-magnetic filler
extracted from the magnetic layer has properties which are the
properties of the colloidal particles described above. The
extraction of the non-magnetic filler from the magnetic layer can
be performed by the following method, for example.
[0125] 1. 1 g of the magnetic layer is scraped off. The scraping
can be performed, for example, by a razor blade.
[0126] 2. A magnetic layer sample obtained by the scraping is put
in a vessel such as an eggplant flask and 100 ml of tetrahydrofuran
is added into this vessel. Examples of tetrahydrofuran include
commercially available tetrahydrofuran to which a stabilizer is
added and commercially available tetrahydrofuran to which a
stabilizer is not added. Meanwhile, here, the commercially
available tetrahydrofuran to which a stabilizer is not added is
used. The same applies to tetrahydrofuran used in washing described
hereinafter.
[0127] 3. A reflux tube is attached to the vessel and heated in a
water bath at a water temperature of 60.degree. C. for 90 minutes.
After filtering the content in the heated vessel with a filter
paper, the solid content remaining on the filter paper is washed
with tetrahydrofuran several times, and the washed solid content is
moved to a vessel such as a beaker. A 4 N (4 mol/L) hydrochloric
acid aqueous solution is added into this vessel and a residue
remaining without being dissolved is extracted by filtering. As a
filter, a filter having a hole diameter smaller than 0.05 .mu.m is
used. For example, a membrane filter used for chromatography
analysis (for example, MF MILLIPORE manufactured by Merck Millipore
Corporation) can be used. The residue extracted by the filtering is
washed with pure water several times and dried.
[0128] Ferromagnetic powder and organic matters (binding agent and
the like) are dissolved by the operation described above, and a
non-magnetic filler is collected as a residue.
[0129] By performing the steps described above, the non-magnetic
filler can be extracted from the magnetic layer. In a case where a
plurality of kinds of non-magnetic fillers are included in the
non-magnetic filler extracted as described above, the plurality of
kinds of non-magnetic fillers can be divided depending on the
differences of density.
[0130] As preferred colloidal particles, inorganic oxide colloidal
particles can be used. As the inorganic oxide colloidal particles,
colloidal particles of inorganic oxide described above can be used,
and composite inorganic oxide colloidal particles such as
SiO.sub.2.Al.sub.2O.sub.3, SiO.sub.2.B.sub.2O.sub.3,
TiO.sub.2.CeO.sub.2, SnO.sub.2.Sb.sub.2O.sub.3,
SiO.sub.2.Al.sub.2O.sub.3.TiO.sub.2, and
TiO.sub.2.CeO.sub.2.SiO.sub.2 can be used. The inorganic oxide
colloidal particles such as SiO.sub.2, Al.sub.2O.sub.3, TiO.sub.2,
ZrO.sub.2, and Fe.sub.2O.sub.3 are preferable and silica colloidal
particles (colloidal silica) are particularly preferable.
Meanwhile, typical colloidal particles have a hydrophilic surface,
and thus, the colloidal particles are suitable for manufacturing a
colloidal solution using water as a dispersion medium. For example,
colloidal silica obtained by a general synthesis method has a
surface covered with polarized oxygen atoms (O.sup.2-), and thus,
colloidal silica adsorbs water in water, forms a hydroxyl group,
and is stabilized. However, these particles are hardly present in a
colloidal state, in an organic solvent normally used in the
magnetic layer forming composition. With respect to this, the
colloidal particles of the invention and the specification are
particles which are not precipitated but are dispersed to cause a
colloidal dispersion, when 1 g thereof is added with respect to 100
mL of the organic solvent described above. Such colloidal particles
can be prepared by a well-known method of hydrophobing the surface
by surface treatment. For details of such hydrophobization
treatment, descriptions disclosed in JP1993-269365A
(JP-H05-269365A), JP1993-287213A (JP-H05-287213A), and
JP2007-63117A are referred to.
[0131] As a manufacturing method of the silica colloidal particles
(colloidal silica) which are preferred colloidal particles, two
kinds of methods such as a water glass method and a sol-gel method
are generally known. The water glass method is a method of using
silica soda (sodium silicate, so-called water glass) as a raw
material, performing ion exchange with respect to this to generate
an active silica, and causing particle growth. Meanwhile, the
sol-gel method is a method of using tetraalkoxysilane as a raw
material, and performing hydrolysis under a basic catalyst and
causing particle growth at the same time. In a case of using the
silica colloidal particles, the silica colloidal particles may be
manufactured by any manufacturing method described above.
[0132] An average particle size of the projection formation agent
is preferably 50 to 200 nm, and more preferably 50 to 150 nm.
[0133] The content of the projection formation agent in the
magnetic layer is preferably 1.0 to 4.0 parts by mass and more
preferably 1.5 to 3.5 parts by mass with respect to 100.0 parts by
mass of the ferromagnetic powder.
[0134] Non-Magnetic Layer
[0135] Next, the non-magnetic layer will be described. The magnetic
tape includes a non-magnetic layer including non-magnetic powder
and a binding agent between the non-magnetic support and the
magnetic layer. The non-magnetic powder used in the non-magnetic
layer may be inorganic powder or organic powder. In addition,
carbon black and the like can also be used. Examples of the
inorganic powder include powders of metal, metal oxide, metal
carbonate, metal sulfate, metal nitride, metal carbide, and metal
sulfide. These non-magnetic powders can be purchased as a
commercially available product or can be manufactured by a
well-known method. For details thereof, descriptions disclosed in
paragraphs 0146 to 0150 of JP2011-216149A can be referred to. For
carbon black which can be used in the non-magnetic layer,
descriptions disclosed in paragraphs 0040 and 0041 of JP2010-24113A
can be referred to. The content (filling percentage) of the
non-magnetic powder of the non-magnetic layer is preferably 50 to
90 mass % and more preferably 60 to 90 mass %.
[0136] In regards to other details of a binding agent or additives
of the non-magnetic layer, the well-known technology regarding the
non-magnetic layer can be applied. In addition, in regards to the
type and the content of the binding agent, and the type and the
content of the additive, for example, the well-known technology
regarding the magnetic layer can be applied.
[0137] The non-magnetic layer of the invention and the
specification also includes a substantially non-magnetic layer
including a small amount of ferromagnetic powder as impurities or
intentionally, together with the non-magnetic powder. Here, the
substantially non-magnetic layer is a layer having a residual
magnetic flux density equal to or smaller than 10 mT, a layer
having coercivity equal to or smaller than 7.96 kA/m (100 Oe), or a
layer having a residual magnetic flux density equal to or smaller
than 10 mT and coercivity equal to or smaller than 7.96 kA/m (100
Oe). It is preferable that the non-magnetic layer does not have a
residual magnetic flux density and coercivity.
[0138] Back Coating Layer
[0139] The magnetic tape can also include a back coating layer
including non-magnetic powder and a binding agent on a side of the
non-magnetic support opposite to the side including the magnetic
layer. The back coating layer preferably includes any one or both
of carbon black and inorganic powder. In regards to the binding
agent included in the back coating layer and various additives
which can be arbitrarily included in the back coating layer, a
well-known technology regarding the treatment of the magnetic layer
and/or the non-magnetic layer can be applied.
[0140] Non-Magnetic Support
[0141] Next, the non-magnetic support (hereinafter, also simply
referred to as a "support") will be described. As the non-magnetic
support, well-known components such as polyethylene terephthalate,
polyethylene naphthalate, polyamide, polyamide imide, aromatic
polyamide subjected to biaxial stretching are used. Among these,
polyethylene terephthalate, polyethylene naphthalate, and polyamide
are preferable. Corona discharge, plasma treatment, easy-bonding
treatment, or thermal treatment may be performed with respect to
these supports in advance.
[0142] Various Thickness
[0143] The total thickness of the magnetic layer and the
non-magnetic layer of the magnetic tape is as described above.
[0144] A thickness of the non-magnetic support of the magnetic tape
is preferably 3.00 to 6.00 .mu.m and more preferably 3.00 to 4.50
.mu.m.
[0145] A thickness of the magnetic layer can be optimized in
accordance with saturation magnetization quantity of the magnetic
head used, a head gap length, or a band of a recording signal. The
thickness of the magnetic layer is normally 0.01 .mu.m to 0.15
.mu.m, and is preferably 0.02 .mu.m to 0.12 .mu.m and more
preferably 0.03 .mu.m to 0.10 .mu.m, from a viewpoint of realizing
recording at high density. The magnetic layer may be at least
single layer, the magnetic layer may be separated into two or more
layers having different magnetic properties, and a configuration of
a well-known multilayered magnetic layer can be applied. A
thickness of the magnetic layer in a case where the magnetic layer
is separated into two or more layers is the total thickness of the
layers.
[0146] A thickness of the non-magnetic layer is, for example, 0.10
to 0.55 .mu.m and is preferably 0.10 to 0.50 .mu.m.
[0147] A thickness of the back coating layer is preferably equal to
or smaller than 0.90 .mu.m and even more preferably 0.10 to 0.70
.mu.m.
[0148] In addition, the total thickness of the magnetic tape is
preferably equal to or smaller than 6.00 .mu.m, more preferably
equal to or smaller than 5.70 .mu.m, and even more preferably equal
to or smaller than 5.50 .mu.m, from a viewpoint of improving
recording capacity for 1 reel of the magnetic tape cartridge.
Meanwhile, the total thickness of the magnetic tape is preferably
equal to or greater than 1.00 .mu.m, from a viewpoint of
availability (handling properties) of the magnetic tape.
[0149] Manufacturing Method of Magnetic Tape
[0150] Preparation of Each Layer Forming Composition
[0151] Each composition for forming the magnetic layer, the
non-magnetic layer, or the back coating layer normally includes a
solvent, together with various components described above. As the
solvent, various organic solvents generally used for manufacturing
a coating type magnetic tape can be used. Among those, from a
viewpoint of solubility of the binding agent normally used in the
coating type magnetic recording medium, each layer forming
composition preferably includes one or more ketone solvents such as
acetone, methyl ethyl ketone, methyl isobutyl ketone, diisobutyl
ketone, cyclohexanone, isophorone, and tetrahydrofuran. The amount
of the solvent of each layer forming composition is not
particularly limited, and can be set to be the same as that of each
layer forming composition of a typical coating type magnetic
recording medium. The steps of preparing a composition for forming
each layer generally include at least a kneading step, a dispersing
step, and a mixing step provided before and after these steps, if
necessary. Each step may be divided into two or more stages. All of
raw materials used in the invention may be added at an initial
stage or in a middle stage of each step. In addition, each raw
material may be separately added in two or more steps. In the
preparation of the magnetic layer forming composition, it is
preferable that the abrasive and the ferromagnetic powder are
separately dispersed as described above. For the preparation method
of the abrasive liquid and the magnetic solution used in the
separate dispersing and the preparation method of the magnetic
layer forming composition, descriptions disclosed in paragraph 0042
to 0048 of JP2014-179149A can be referred to. In addition, in order
to manufacture the magnetic tape, a well-known manufacturing
technology can be used. In the kneading step, an open kneader, a
continuous kneader, a pressure kneader, or a kneader having a
strong kneading force such as an extruder is preferably used. The
details of the kneading processes of these kneaders are disclosed
in JP1989-106338A (JP-H01-106338A) and JP1989-79274A
(JP-H01-79274A). In addition, in order to disperse each layer
forming composition, glass beads and one or more kinds of other
dispersion beads can be used as a dispersion medium. As such
dispersion beads, zirconia beads, titania beads, and steel beads
which are dispersion beads having high specific gravity are
suitable. These dispersion beads can be used by optimizing a
particle diameter (bead diameter) and a filling percentage of the
dispersion beads. As a dispersion device, a well-known dispersion
device can be used. The each layer forming composition may be
filtered by a well-known method before performing the coating step.
The filtering can be performed by using a filter, for example. As
the filter used in the filtering, a filter having a hole diameter
of 0.01 to 3 .mu.m can be used, for example.
[0152] In addition, the FWHM.sub.after measured after the vacuum
heating tends to be decreased, in a case where the dispersion
conditions of the magnetic layer forming composition are reinforced
(for example, the number of times of the dispersion is increased,
the dispersion time is extended, and the like), and/or the
filtering conditions are reinforced (for example, a filter having a
small hole diameter is used as a filter used in the filtering, the
number of times of the filtering is increased, and the like). The
inventors have surmised that this is because the uniformity of the
height of the projection present on the surface of the magnetic
layer is improved, by improving dispersibility and/or the
uniformity of the particle size of the powder included in the
magnetic layer forming composition, particularly, the non-magnetic
filler which may function as the projection formation agent
described above. In one aspect, a preliminary experiment can be
performed before the actual manufacturing, and the dispersion
conditions and/or the filtering conditions can be optimized.
[0153] In addition, in the magnetic tape including the magnetic
layer including carbon black as the non-magnetic filler, it is
effective to use the dispersing agent for improving dispersibility
of the carbon black as a magnetic layer component, in order to
decrease the FWHM.sub.after measured after the vacuum heating. For
example, organic tertiary amine can be used as a dispersing agent
of carbon black. For details of the organic tertiary amine,
descriptions disclosed in paragraphs 0011 to 0018 and 0021 of
JP2013-049832A can be referred to. The organic tertiary amine is
more preferably trialkylamine. An alkyl group included in
trialkylamine is preferably an alkyl group having 1 to 18 carbon
atoms. Three alkyl groups included in trialkylamine may be the same
as each other or different from each other. For details of the
alkyl group, descriptions disclosed in paragraphs 0015 and 0016 of
JP2013-049832A can be referred to. As trialkylamine, trioctylamine
is particularly preferable.
[0154] Coating Step
[0155] The magnetic layer can be formed by performing multilayer
coating of the magnetic layer forming composition with the
non-magnetic layer forming composition in order or at the same
time. The back coating layer can be formed by applying the back
coating layer forming composition to a side of the non-magnetic
support opposite to a side provided with the magnetic layer (or to
be provided with the magnetic layer). For details of the coating
for forming each layer, a description disclosed in a paragraph 0066
of JP2010-231843A can be referred to.
[0156] Other Steps
[0157] For details of various other steps for manufacturing the
magnetic tape, descriptions disclosed in paragraphs 0067 to 0070 of
JP2010-231843A can be referred to.
[0158] One Aspect of Preferred Manufacturing Method
[0159] As a preferred manufacturing method, a manufacturing method
of applying vibration to the magnetic layer can be used, in order
to improve uniformity of the thickness of the liquid film formed of
fatty acid ester on the surface of the magnetic layer. The
inventors have surmised that, by adding vibration, the liquid film
formed of fatty acid ester on the surface of the magnetic layer
flows and the uniformity of the thickness of the liquid film is
improved.
[0160] That is, the magnetic tape can be manufactured by a
manufacturing method including: forming the magnetic layer by
applying the magnetic layer forming composition including
ferromagnetic powder, a binding agent, an abrasive, and fatty acid
ester, with the non-magnetic layer forming composition in order or
at the same time, and drying; and applying vibration to the formed
magnetic layer. The manufacturing method is identical to the
typical manufacturing method of the magnetic tape, except for
applying vibration to the magnetic layer, and the details thereof
are as described above.
[0161] Means for applying vibration are not particularly limited.
For example, the vibration can be applied to the magnetic layer, by
bringing the surface of the non-magnetic support, provided with the
magnetic layer formed, on a side opposite to the magnetic layer to
come into contact with a vibration imparting unit. The non-magnetic
support, provided with the magnetic layer formed, may run while
coming into contact with a vibration imparting unit. The vibration
imparting unit, for example, includes an ultrasonic vibrator
therein, and accordingly, vibration can be applied to a product
coming into contact with the unit. It is possible to adjust the
vibration applied to the magnetic layer by a vibration frequency,
and strength of the ultrasonic vibrator, and/or the contact time
with the vibration imparting unit. For example, the contact time
can be adjusted by a running speed of the non-magnetic support,
provided with the magnetic layer formed, while coming into contact
with the vibration imparting unit. The vibration imparting
conditions are not particularly limited, and may be set so as to
control the full width at half maximum of the spacing distribution,
particularly, the FWHM.sub.before. In order to set the vibration
imparting conditions, a preliminary experiment can be performed
before the actual manufacturing, and the conditions can be
optimized.
[0162] As described above, it is possible to obtain a magnetic tape
according to one aspect of the invention. However, the
manufacturing method described above is merely an example, the
state of the abrasive present in the magnetic layer, the
FWHM.sub.before, the FWHM.sub.after, and the difference
(S.sub.after-S.sub.before) can be controlled to be in respective
ranges described above by an arbitrary method capable of adjusting
the state of the abrasive present in the magnetic layer, the
FWHM.sub.before, the FWHM.sub.after, and the difference
(S.sub.after-S.sub.before), and such an aspect is also included in
the invention.
[0163] The magnetic tape according to one aspect of the invention
described above is generally accommodated in a magnetic tape
cartridge and the magnetic tape cartridge is mounted in a drive.
The configuration of the magnetic tape cartridge and the drive is
well known. The magnetic tape runs (is transported) in the drive,
the magnetic head for recording and/or reproducing of information
comes into contact with and slides on the surface of the magnetic
layer, and the recording of the information on the magnetic tape
and/or reproducing of the recorded information are performed. In
the magnetic tape, although the total thickness of the non-magnetic
layer and the magnetic layer is equal to or smaller than 0.60
.mu.m, it is possible to prevent a deterioration of electromagnetic
conversion characteristics while repeating the running in a low
temperature and high humidity environment.
EXAMPLES
[0164] Hereinafter, the invention will be described with reference
to examples. However, the invention is not limited to aspects shown
in the examples. "Parts" and "%" in the following description mean
"parts by mass" and "mass %", unless otherwise noted. In addition,
steps and evaluations described below are performed in an
environment of an atmosphere temperature of 23.degree.
C..+-.1.degree. C., unless otherwise noted.
[0165] Preparation Examples of Ferromagnetic Hexagonal Ferrite
Powders
[0166] In the method disclosed in Example 1 of JP2011-225417A, an
Al adhesion amount was adjusted by changing the amount of
Al.sub.2O.sub.3 added to a raw material mixture, a particle size
was adjusted by changing a crystallization temperature, and
ferromagnetic hexagonal ferrite powders (barium ferrite powders) in
which Al.sub.2O.sub.3 was adhered to the surface of the particle
were manufactured.
[0167] Regarding the prepared ferromagnetic hexagonal ferrite
powders, in a case where an average particle size (average plate
diameter) was acquired by the method described above, it was 25
nm.
[0168] In addition, regarding the prepared ferromagnetic hexagonal
ferrite powders, the Al content was measured and the Al presence
state was confirmed by the method disclosed in a paragraph 0070 of
JP2014-179149A. The Al content of the prepared ferromagnetic
hexagonal ferrite powders was 3.0 mass % in terms of
Al.sub.2O.sub.3 with respect to 100.0 mass % which is the total
mass of the ferromagnetic hexagonal ferrite powder used in the
measurement. In addition, in the prepared ferromagnetic hexagonal
ferrite powders, it was confirmed that Al is adhered onto the
primary particles (specifically, a coated film including Al is
present).
Example 1
[0169] 1. Preparation of Alumina Dispersion (Abrasive Liquid)
[0170] 2,3-dihydroxynaphthalene (manufactured by Tokyo Chemical
Industry Co., Ltd.) having the amount shown in Table 1, 31.3 parts
of 32% solution (solvent is a mixed solvent of methyl ethyl ketone
and toluene) of a polyester polyurethane resin having a SO.sub.3Na
group as a polar group (UR-4800 manufactured by Toyobo Co., Ltd.
(amount of a polar group: 80 meq/kg)), and 570.0 parts of a mixed
solution of methyl ethyl ketone and cyclohexanone at 1:1 (mass
ratio) as a solvent were mixed with 100.0 parts of alumina powder
(Mohs hardness of 9) having a gelatinization ratio of approximately
65% and a BET specific surface area shown in Table 1, and dispersed
in the presence of zirconia beads by a paint shaker for the time
(bead dispersion time) shown in Table 1. After the dispersion, the
dispersion liquid and the beads were separated by a mesh and an
alumina dispersion (abrasive liquid) was obtained.
[0171] 2. Magnetic Layer Forming Composition List
[0172] Magnetic Solution
[0173] Ferromagnetic hexagonal barium ferrite powder prepared in
the preparation example: 100.0 parts
[0174] SO.sub.3Na group-containing polyurethane resin: 14.0 parts
[0175] (Weight-average molecular weight: 70,000, SO.sub.3Na group:
0.2 meq/g)
[0176] Cyclohexanone: 150.0 parts
[0177] Methyl ethyl ketone: 150.0 parts
[0178] Abrasive Liquid
[0179] Alumina dispersion prepared in the section 1.: 6.0 parts
[0180] Silica Sol (Projection Forming Agent Liquid)
[0181] Colloidal silica (average particle size of 100 nm): 2.0
parts
[0182] Methyl ethyl ketone: 1.4 parts
[0183] Other Components
[0184] Stearic acid: 2.0 parts
[0185] Butyl stearate: see Table 1
[0186] Polyisocyanate (CORONATE (registered trademark) manufactured
by Nippon Polyurethane Industry Co., Ltd.): 2.5 parts
[0187] Finishing Additive Solvent
[0188] Cyclohexanone: 200.0 parts
[0189] Methyl ethyl ketone: 200.0 parts
[0190] 3. Non-Magnetic Layer Forming Composition List
[0191] Non-magnetic inorganic powder: .alpha.-iron oxide: 100.0
parts
[0192] Average particle size (average long axis length): 0.15
.mu.m
[0193] Average acicular ratio: 7
[0194] BET specific surface area: 52 m.sup.2/g
[0195] Carbon black: 20.0 parts
[0196] Average particle size: 20 nm
[0197] An electron beam-curable vinyl chloride copolymer: 13.0
parts
[0198] An electron beam-curable polyurethane resin: 6.0 parts
[0199] Stearic acid: 1.0 part
[0200] Butyl stearate: see Table 1
[0201] Cyclohexanone: 300.0 parts
[0202] Methyl ethyl ketone: 300.0 parts
[0203] 4. Back Coating Layer Forming Composition List
[0204] Non-magnetic inorganic powder: .alpha.-iron oxide: 80.0
parts
[0205] Average particle size (average long axis length): 0.15
.mu.m
[0206] Average acicular ratio: 7
[0207] BET specific surface area: 52 m.sup.2/g
[0208] Carbon black: 20.0 parts
[0209] Average particle size: 20 nm
[0210] A vinyl chloride copolymer: 13.0 parts
[0211] Sulfonic acid group-containing polyurethane resin: 6.0
parts
[0212] Phenylphosphonic acid: 3.0 parts
[0213] Methyl ethyl ketone: 155.0 parts
[0214] Stearic acid: 3.0 parts
[0215] Butyl stearate: 3.0 parts
[0216] Polyisocyanate: 5.0 parts
[0217] Cyclohexanone: 355.0 parts
[0218] 5. Preparation of Each Layer Forming Composition
[0219] (1) Preparation of Magnetic Layer Forming Composition
[0220] The magnetic layer forming composition was prepared by the
following method.
[0221] A magnetic solution was prepared by performing beads
dispersing of the magnetic solution components described above by
using beads as the dispersion medium in a batch type vertical sand
mill. Specifically, the beads dispersion was performed for the
dispersion retention time shown in Table 1 by using zirconia beads
(bead diameter: 0.1 mm).
[0222] The magnetic solution obtained as described above, the
abrasive liquid, silica sol, other components, and the finishing
additive solvent were introduced into a dissolver stirrer, and were
stirred at a circumferential speed of 10 m/sec for 30 minutes.
After that, the treatment was performed with a flow type ultrasonic
dispersing device at a flow rate of 7.5 kg/min for the number of
times of the passes shown in Table 1, and then, a magnetic layer
forming composition was prepared by performing filtering with a
filter having a hole diameter shown in Table 1, for the number of
times of the passes shown in Table 1.
[0223] (2) Preparation of Non-Magnetic Layer Forming
Composition
[0224] The non-magnetic layer forming composition was prepared by
the following method.
[0225] Each component excluding stearic acid, butyl stearate,
cyclohexanone, and methyl ethyl ketone was beads-dispersed by using
a batch type vertical sand mill (dispersion medium: zirconia beads
(bead diameter: 0.1 mm), dispersion retention time: 24 hours) to
obtain dispersion liquid. After that, the remaining components were
added into the obtained dispersion liquid and stirred with a
dissolver. Then, the obtained dispersion liquid was filtered by
using the filter (hole diameter of 0.5 .mu.m), and a non-magnetic
layer forming composition was prepared.
[0226] (3) Preparation of Back Coating Layer Forming
Composition
[0227] The back coating layer forming composition was prepared by
the following method.
[0228] Each component excluding stearic acid, butyl stearate,
polyisocyanate, and cyclohexanone was kneaded and diluted by an
open kneader. Then, the obtained mixed solution was subjected to a
dispersing process of 12 passes, with a transverse beads mill by
using zirconia beads having a bead diameter of 1.0 mm, by setting a
bead filling percentage as 80 volume %, a circumferential speed of
rotor distal end as 10 m/sec, and a retention time for 1 pass as 2
minutes. After that, the remaining components were added into the
obtained dispersion liquid and stirred with a dissolver. Then, the
obtained dispersion liquid was filtered with a filter (hole
diameter: 1.0 .mu.m) and a back coating layer forming composition
was prepared.
[0229] 6. Manufacturing of Magnetic Tape
[0230] The non-magnetic layer forming composition was applied onto
a polyethylene naphthalate support having a thickness shown in
Table 1 and dried so that the thickness after the drying becomes a
thickness shown in Table 1, and then, an electron beam was emitted
with an energy of 40 kGy at an acceleration voltage of 125 kV. The
magnetic layer forming composition was applied so that the
thickness after the drying becomes a thickness shown in Table 1 and
dried to form a coating layer of the magnetic layer forming
composition.
[0231] After that, the support, provided with the coating layer
formed, was installed in a vibration imparting device shown in FIG.
1 so that the surface thereof on a side opposite to the surface
where the coating layer is formed comes into contact with the
vibration imparting unit, and the support (in FIG. 1, reference
numeral 1), provided with the coating layer formed, was transported
at a transportation speed of 0.5 m/sec, to apply vibration to the
coating layer. In FIG. 1, a reference numeral 2 denotes a guide
roller (a reference numeral 2 denotes one of two guide rollers), a
reference numeral 3 denotes the vibration imparting device
(vibration imparting unit including the ultrasonic vibrator), and
an arrow denotes a transportation direction. The time from the
start of the contact of the arbitrary portion of the support,
provided with the coating layer formed, with the vibration
imparting unit until the end of the contact is shown in Table 1 as
the vibration imparting time. The vibration imparting unit used
includes an ultrasonic vibrator therein. The vibration was imparted
by setting a vibration frequency and the intensity of the
ultrasonic vibrator as values shown in Table 1.
[0232] After that, the back coating layer forming composition was
applied onto the surface of the support on a side opposite to the
surface where the non-magnetic layer and the magnetic layer are
formed, and dried so that the thickness after the drying becomes
thickness shown in Table 1.
[0233] After that, the surface smoothing treatment (calender
process) was performed with a calender roll configured of only a
metal roll, at a calender process speed of 80 m/min, linear
pressure of 300 kg/cm (294 kN/m), and a surface temperature of a
calender roll of 95.degree. C.
[0234] Then, the thermal treatment was performed in the environment
of the atmosphere temperature of 70.degree. C. for 36 hours. After
the thermal treatment, the slitting was performed so as to have a
width of 1/2 inches (0.0127 meters), and the surface of the
magnetic layer was cleaned with a tape cleaning device in which a
nonwoven fabric and a razor blade are attached to a device
including a sending and winding device of the slit so as to press
the surface of the magnetic layer.
[0235] By doing so, a magnetic tape was manufactured.
Examples 2 to 8 and Comparative Examples 1 to 12
[0236] Each magnetic tape of Examples 2 to 8 and Comparative
Examples 1 to 12 was obtained in the same manner as in Example 1,
except that the manufacturing conditions were changed as shown in
Table 1. The vibration imparting time was adjusted by changing the
transportation speed of the support on which the coating layer of
the magnetic layer forming composition was formed.
[0237] A part of each magnetic tape of Examples 1 to 8 and
Comparative Examples 1 to 12 obtained by the steps described above
was used in the evaluation of physical properties described below,
and the other part was used in the evaluation of performance which
will be described later. The thickness of each layer of each
magnetic tape and the non-magnetic support of Examples 1 to 8 and
Comparative Examples 1 to 12 was acquired by the following method.
It was confirmed that the thicknesses of the formed layer and the
non-magnetic support was the thicknesses shown in Table 1.
[0238] A cross section of the magnetic tape in a thickness
direction was exposed to ion beams and the exposed cross section
was observed with a scanning electron microscope. Various
thicknesses were obtained as an arithmetical mean of thicknesses
obtained at two portions in the thickness direction in the cross
section observation.
[0239] 7. Evaluation of Physical Properties
[0240] (1) State of Abrasive Present in Magnetic Layer (Plan View
Maximum Area Percentage of Abrasive)
[0241] By the method described above, the plan view maximum area
percentage of the abrasive confirmed in a region having a size of
4.3 .mu.m.times.6.3 .mu.m of the surface of the magnetic layer is
acquired.
[0242] (2) FWHM.sub.before and FWHM.sub.after
[0243] The full width at half maximum of the spacing distributions
FWHM.sub.before and FWHM.sub.after before and after vacuum heating
were acquired by the following method by using a tape spacing
analyzer (TSA) (manufactured by Micro Physics, Inc.).
[0244] In a state where a glass plate included in the TSA was
disposed on the surface of the magnetic layer of the magnetic tape,
a hemisphere was pressed against the surface of the back coating
layer of the magnetic tape at a pressure of 5.05.times.10.sup.4 N/m
(0.5 atm) by using a hemisphere made of urethane included in the
TSA as a pressing member. In this state, a given region (150,000 to
200,000 .mu.m.sup.2) of the surface of the magnetic layer of the
magnetic tape was irradiated with white light from a stroboscope
included in the TSA through the glass plate, and the obtained
reflected light was received by a charge-coupled device (CCD)
through an interference filter (filter selectively passing light at
a wavelength of 633 nm), and thus, an interference fringe image
generated on the uneven part of the region was obtained.
[0245] This image was divided into 300,000 points, a distance
(spacing) between the surface of the glass plate on the magnetic
tape side and the surface of the magnetic layer of the magnetic
tape was acquired, and the full width at half maximum of spacing
distribution was full width at half maximum, in a case where this
spacing was shown with a histogram, and this histogram was fit with
Gaussian distribution.
[0246] The vacuum heating was performed by storing the magnetic
tape in a vacuum constant temperature drying machine with a degree
of vacuum of 200 Pa to 0.01 Mpa and at inner atmosphere temperature
of 70.degree. C. to 90.degree. C. for 24 hours.
[0247] (3) Difference (S.sub.after-S.sub.before)
[0248] The difference (S.sub.after-S.sub.before) was a value
obtained by subtracting a mode of the histogram before the vacuum
heating from a mode of the histogram after the vacuum heating
obtained in the section (2).
[0249] 8. Evaluation of Performance (Change (Decrease of SNR) in
Electromagnetic Conversion Characteristics (Signal-To-Noise-Ratio
(SNR)) After Repeated Running in Low Temperature and High Humidity
Environment)
[0250] The electromagnetic conversion characteristics (SNR) were
measured by the following method by using a reel tester having a
width of 1/2 inches (0.0127 meters) and including a fixed head.
[0251] A head/tape relative speed was set as 5.5 m/sec, a
metal-in-gap (MIG) head (gap length of 0.15 .mu.m, track width of
1.0 .mu.m) was used in the recording, and a recording current was
set as an optimal recording current of each magnetic tape. As a
reproducing head, a giant-magnetoresistive (GMR) head having an
element thickness of 15 nm, a shield interval 0.1 .mu.m and a lead
width of 0.5 .mu.m was used. The recording of a signal was
performed at linear recording density of 270 KFci, and measurement
regarding a reproduction signal was performed with a spectrum
analyzer manufactured by Shibasoku Co., Ltd. The unit, kfci, is a
unit of linear recording density (not able to convert to the SI
unit system). Regarding the signal, a signal which was sufficiently
stabilized after starting the running of the magnetic tape was
used. A ratio of an output value of a carrier signal and integrated
noise of the entire spectral range was set as a SNR.
[0252] Under the conditions described above, a tape length for 1
pass was set as 1,000 m, the reciprocating running for 5,000 passes
was allowed in an environment of an atmosphere temperature of
13.degree. C. and relative humidity of 80% to perform reproduction
(head/tape relative speed: 6.0 m/sec), and the SNR was measured. A
difference between the SNR of the first pass and the SNR of the
5,000-th pass (SNR of the 5,000-th pass-SNR of the first pass) was
acquired. In a case where the difference is less than -2.0 dB, the
magnetic tape can be determined as a magnetic tape which shows
excellent electromagnetic conversion characteristics desired in a
data back-up tape.
[0253] The results of the evaluations described above are shown in
Table 1.
TABLE-US-00001 TABLE 1 Magnetic layer forming composition
preparation Ultrasonic vibration imparting conditions Content of
butyl conditions Number of times Number stearate (part) Vibration
of passes of flow of times Magnetic layer Non-magnetic imparting
Vibration type ultrasonic of Filter hole forming layer forming time
frequency Intensity dispersing device filtering diameter
composition composition (sec) (kHz) (W) (times) (times) (.mu.m)
Comparative Example 1 1.0 4.0 None None None 2 1 1.0 Comparative
Example 2 1.0 4.0 None None None 2 1 1.0 Comparative Example 3 1.0
4.0 None None None 2 1 1.0 Comparative Example 4 1.0 4.0 None None
None 2 1 1.0 Comparative Example 5 1.0 4.0 None None None 2 1 1.0
Comparative Example 6 1.0 4.0 None None None 2 1 1.0 Comparative
Example 7 1.0 4.0 None None None 2 1 1.0 Comparative Example 8 1.0
4.0 0.5 30 100 1 1 1.0 Comparative Example 9 1.0 10.0 0.5 30 100 2
1 1.0 Comparative Example 10 0 0 0.5 30 100 2 1 1.0 Comparative
Example 11 1.0 4.0 0.5 30 100 2 1 1.0 Comparative Example 12 1.0
4.0 0.5 30 100 2 1 1.0 Example 1 1.0 4.0 0.5 30 100 2 1 1.0 Example
2 1.0 4.0 3.0 30 100 2 1 1.0 Example 3 1.0 4.0 0.5 30 100 30 5 0.5
Example 4 1.0 4.0 0.5 30 100 2 1 1.0 Example 5 1.0 4.0 0.5 30 100 2
1 1.0 Example 6 1.0 4.0 0.5 30 100 2 1 1.0 Example 7 1.0 4.0 0.5 30
100 2 1 1.0 Example 8 1.0 4.0 3.0 30 100 30 5 0.5 Treatment
conditions after mixing of magnetic solution abrasive liquid,
silica Abrasive liquid sol, other components and Abrasive Abrasive
liquid finishing additive solvent BET Beads dispersing agent Beads
specific dispersion (2,3-Dihydroxynaphthalene) dispersion
Ultrasonic surface area time content time dispersion time Filter
hole (m.sup.2/g) (hour) (part) (min) (min) diameter Comparative
Example 1 20 5 0 5 0.5 0.5 .mu.m Comparative Example 2 20 5 0 5 0.5
0.5 .mu.m Comparative Example 3 20 5 0 5 0.5 0.5 .mu.m Comparative
Example 4 20 5 0 5 0.5 0.5 .mu.m Comparative Example 5 20 5 1.0 60
30 0.5 .mu.m Comparative Example 6 20 30 3.0 60 30 0.5 .mu.m
Comparative Example 7 30 30 3.0 180 60 0.3 .mu.m Comparative
Example 8 20 30 3.0 60 30 0.5 .mu.m Comparative Example 9 20 30 3.0
60 30 0.5 .mu.m Comparative Example 10 20 30 3.0 60 30 0.5 .mu.m
Comparative Example 11 20 5 0 5 0.5 0.5 .mu.m Comparative Example
12 30 30 5.0 360 60 0.3 .mu.m Example 1 20 5 1.0 60 30 0.5 .mu.m
Example 2 20 5 1.0 60 30 0.5 .mu.m Example 3 20 5 1.0 60 30 0.5
.mu.m Example 4 20 30 3.0 60 30 0.5 .mu.m Example 5 30 30 3.0 180
60 0.3 .mu.m Example 6 20 30 3.0 60 30 0.5 .mu.m Example 7 20 30
3.0 60 30 0.5 .mu.m Example 8 30 30 3.0 180 60 0.3 .mu.m
Non-magnetic layer + Magnetic layer Non-magnetic layer Non-magnetic
support Back coating layer magnetic layer Thickness Thickness
Thickness Thickness Total thickness (.mu.m) (.mu.m) (.mu.m) (.mu.m)
(.mu.m) Comparative Example 1 0.10 1.00 4.30 0.60 1.10 Comparative
Example 2 0.10 0.70 4.30 0.60 0.80 Comparative Example 3 0.10 0.50
4.30 0.60 0.60 Comparative Example 4 0.10 0.10 4.30 0.60 0.20
Comparative Example 5 0.10 0.50 4.30 0.60 0.60 Comparative Example
6 0.10 0.50 4.30 0.60 0.60 Comparative Example 7 0.10 0.50 4.30
0.60 0.60 Comparative Example 8 0.10 0.50 4.30 0.60 0.60
Comparative Example 9 0.10 0.50 4.30 0.60 0.60 Comparative Example
10 0.10 0.50 4.30 0.60 0.60 Comparative Example 11 0.10 0.50 4.30
0.60 0.60 Comparative Example 12 0.10 0.50 4.30 0.60 0.60 Example 1
0.10 0.50 4.30 0.60 0.60 Example 2 0.10 0.50 4.30 0.60 0.60 Example
3 0.10 0.50 4.30 0.60 0.60 Example 4 0.10 0.50 4.30 0.60 0.60
Example 5 0.10 0.50 4.30 0.60 0.60 Example 6 0.10 0.10 4.30 0.60
0.20 Example 7 0.10 0.50 4.30 0.60 0.60 Example 8 0.10 0.50 4.30
0.60 0.60 Evaluation result Percentage of plan view maximum area
Decrease in SNR S.sub.after - S.sub.before (nm) FWHM.sub.before
(nm) FWHM.sub.after (nm) of abrasive (dB) Comparative Example 1 6.0
8.6 6.8 0.06% -0.3 Comparative Example 2 4.2 8.6 6.8 0.06% -0.5
Comparative Example 3 3.2 8.6 6.8 0.06% -3.3 Comparative Example 4
1.0 8.6 6.8 0.06% -5.6 Comparative Example 5 3.2 8.6 6.8 0.05% -3.2
Comparative Example 6 3.2 8.6 6.8 0.04% -4.5 Comparative Example 7
3.2 8.6 6.8 0.02% -5.9 Comparative Example 8 3.2 6.8 7.5 0.04% -3.1
Comparative Example 9 8.4 6.8 6.8 0.04% -5.0 Comparative Example 10
0 6.8 6.8 0.04% -3.0 Comparative Example 11 3.2 6.8 6.8 0.06% -4.2
Comparative Example 12 3.2 6.8 6.8 0.01% -2.5 Example 1 3.2 6.8 6.8
0.05% -0.7 Example 2 3.2 4.0 6.8 0.05% -0.5 Example 3 3.2 6.8 4.0
0.05% -0.2 Example 4 3.2 6.8 6.8 0.04% -0.8 Example 5 3.2 6.8 6.8
0.02% -0.6 Example 6 3.2 6.8 6.8 0.04% -0.4 Example 7 3.2 6.8 6.8
0.04% -0.5 Example 8 3.2 4.0 4.0 0.02% -0.3
[0254] With the comparison of Comparative Examples, it was
confirmed that, in the case where the total thickness of the
non-magnetic layer and the magnetic layer is equal to or smaller
than 0.60 .mu.m (Comparative Examples 3 to 12), the SNR is
significantly decreased by the repeated running in a low
temperature and high humidity environment, compared to the case
where the total thickness of the non-magnetic layer and the
magnetic layer exceeds 0.60 .mu.m (Comparative Examples 1 and
2).
[0255] In a case where a reproducing head after evaluation of the
magnetic tape of the comparative example was visually observed, in
a reproducing head (GMR head) of Comparative Examples 3, 4, and 11
after the evaluation, it was confirmed that a phenomenon called
pole tip recession (PTR) in which a difference in level of an
element portion and a sliding surface of a GMR head occurs. It is
assumed that the PTR is generated due to the chipping of the
element part of the GMR head caused by the sliding on the surface
of the magnetic layer. Meanwhile, in the reproducing head of
Comparative Examples 5 to 8, 10, and 12 after the evaluation, it
was confirmed that the head attached materials were attached to the
GMR head. It is assumed that, in Comparative Examples 5 to 8 and
10, the scraps generated due to chipping of the surface of the
magnetic layer become head attached materials. It is considered
that, in Comparative Example 12, in a case where the abrasion
properties of the surface of the magnetic layer are not
sufficiently exhibited, the head attached materials are not
removed.
[0256] In Comparative Example 9, it is thought that a reason of a
significant decrease in SNR due to the repeated running in the low
temperature and high humidity environment is the occurrence of
sticking between the surface of the magnetic layer and the
reproducing head.
[0257] With respect to this, in the magnetic tape of Examples 1 to
8, the total thickness of the non-magnetic layer and the magnetic
layer was equal to or smaller than 0.60 .mu.m, but a decrease in
SNR was prevented, compared to the magnetic tape of Comparative
Examples 3 to 12.
[0258] The invention is effective in technical fields of magnetic
tapes for high-density recording.
* * * * *